If you Smite it you get health back. If you deal the killing blow to it you get Crest of Cinders from it.

Using Smite on the Red Brambleback

Using Smite on the Red Brambleback will restore a large amount of health instantly (20% of your maximum health). This bonus can only be claimed once per spawn.

The Red Brambleback gives off green bubbles if the Smite bonus is available. Once the bonus is harvested, the effect disappears until the Red Brambleback respawns. This is only visible to champions with Smite.

Gaining health by smiting the Red Brambleback is something they added in S5. It is handy for jungle sustain for just about every jungler at any stage of the game because of the % health restoration.

Smiting it on your first clear is going to be a matter of preference. Ask yourself if you need the health to accomplish your planned jungle route. If your plan is to start Gromp, clear blue, and then red, and gank if there are opportunities on the map and the health will put you in a healthier state for the gank then by all means smite it.

Later in the game you'll probably want to save your Smite for Champions (assuming you have a champion targetable smite), Major Objectives (such as Dragon and Baron), Raptors, Gromp, Minor Objectives (such as your enemies' Raptors or Murkwolves).

But if you are in dire need of health and it is not an opportune time to back then go for it. If you are donating it and are low on health you can even choose to start with Smite to obtain the health before letting your ADC/carry deal the killing blow to it.

Dealing the Killing Blow
This unit's physical attacks apply a debuff that slows the target's movement speed by 8 / 16 / 24% (5 / 10 / 15% for ranged attacks) for 3 seconds and a DoT that deals 8 + (2 × level) bonus true damage twice. Also heals buff holder by 1% of their maximum health per 5 seconds. If the buff holder is slain, this buff is transferred to the killer. (the amount slowed is modified by your champions level with 8% at level 1, 16% at level 6, and 24% at level 11).

Duration is 2 min or 2 min 24 s with Runic Affinity

Clearing
Increases clear speed and helps with sustain on clears. If you are comfortable with the amount of damage the DOT effect does you can let the last ticks of damage from the buff kill the last camp creep(s) and continue on your jungle route.

Ganking
An 8% slow isn't much. But in the hands of an autoattack based champion such as Lee Sin the DOT can add up to quite a bit of damage and the minor slow helps keep the enemy laner in range for autoattacks just a bit longer. It should be noted that abilities (except for certain abilities that apply On-Hit effects such as Gangplank's Q, Parrrley) don't apply the slow. You have to autoattack your target to apply the slow, so make sure to include auto's in your rotation while trying to take the enemy laner down. Another point is that slowed enemies are easier to hit with skill shots, so try to apply the slow before using your skill shots on them.

Red buff is particularly useful for junglers that don't otherwise sport any Crowd Control before level 6 such as Shyvana.

Given that Stalker's Blade is in the game and attainable after clearing half of your jungle we need to talk about how slows stack.

I'm going to steal this section from a post I found by GuraKKa at Do Slow Effects Stack? which was orginially sourced to LoL Wikia, but doesn't appear to exist as a page by itself any longer that I can tell.

Quoted:

Slowing effects follow particular rules when stacking:

If a champion is affected by multiple slows, the strongest one will be fully applied, while the others are applied sequentially with 65% reduced effectiveness down to 35% of its original strength.
Slow effects derived from items' passives do NOT stack, even when coming from different champions. Only the strongest item slow is applied at any moment. The exception to this is the active effect of Randuin's Omen, Hextech Gunblade and Bilgewater Cutlass, which stacks with other slowing items normally because they are considered champion abilities for slow stacking purposes.
Attacking a champion with the Blessing of the Lizard Elder buff when the target is already affected by that slow will reapply the debuff, resetting its duration. It will NOT increase the slow amount. The same holds true for the Exhaust summoner spell.

ExampleEdit

A champion with a raw movement speed of 400 is affected by a 2 second long 40% slow and a 5 second long 20% slow at the same time.

For the first two seconds, he will have (1 − 0.4) × (1 − 0.2 × 0.35) = 0.6 × 0.93 = 55.8% of his original movement speed (a 44.2% effective slow). So he will have 400 × 0.558 = 223.2 raw movement speed.
For the following three seconds, the effective slow will be 20% and so he will have 400 × 0.8 = 320 movement speed.
After that, he will return to his normal speed of 400.


Clear as mud? I thought so. Basically slows stack but there are diminishing returns. So you can look at it a couple of ways.

If you have bursty champs such as Jax and Rengar and you think you can kill your target in one set of ability rotations then stacking your slows probably makes the most sense.

If you have champions that are better at dealing damage over time and you have room in the lane, then staggering your slows may give you the best opportunity for securing a kill.

However given that Chilling Smite is ranged and The Crest of Cinders slow debuff is applied through autoattacks the natural order is going to be Chilling Smite for a 20% slow and and you will follow up with autoattacks that apply an 8% slow.

Donating The Crest of Cinders
When team fights start to break out you are going to want to donate Red buff to a carry on your team. Usually this will be your ADC as they can apply the true damage over time and slow debuff through ranged autoattacks and they have a lot of attack speed so they can get the debuff applied to more targets faster. It also allows your ADC who is a prime target in team fights to better kite enemies that go after them.