This is a very good question, it was never a viable choice in the previous season because, as a support, it would be very difficult for you to buy items that would effectively affectt a team fight. But this is over, and with the new season supports are able make as much money as a jungler, if not more, so you are now capable of doing a decent build on supports and have a direct impact in your team, not just by having utility.

In the end of this guide i will present you the reasons (numbers to everything i'm explaining)

Your job is to bully the other duo comp out of the lane and make them farm under the turret. The high mobility, sustain and output of Tarick is just to damn perfect now. Ask your adc to bring sweeping lens so you can control the vision in your lane, if you play this correctly you can both buy pink wards and have your plane permanentely warded and safe (tribushh and river) and you can minimize all incoming ganks of the laning phase to about 1 or 2 pinks meaning a lot more money for you to spend in items.

So you understand the mechanics of tarick the perfect combo on him is the following:

E > W > Auto-Attack > Q (your ADC) > Auto-Attack

As said above, try to reach level 2 before your enemies and then go after them. E the carry and then walk to him W and auto-attack. In level 2 this should take about 1/4 or 1/3 of his life and if your ADC follows and autos 2 times he will have less than 1/3 of his life.

Then, just repeat the process.

In Team Fight - in most cases you should always be the frontline of your team and your E is the perfect counter-engager or engager. But there are some different cases that you always have to consider.

1 Case - They have an assassin:
If done your job correctly your ADC well most likely be fed and since he can output the most damage your main concern should always be him. If they have a Zed, Fizz Talon etc you should always save your Stun (E) to stop their combo and make sure your ADC lives.

2 Case - Heavy CC Team:
Heavy CC teams are always a "pain in the ***", but your stun is just perfect to disable any attept. I.E. a zack slingshots to your team, always try to land your Stun before he ults, that way he will wither die or have to use it to get out of the team fight leaving the team exposed.

2 Case - Your team is way ahead:
Then its all up to you to engage. One of the most common mistakes i see teams doing is by letting underlevel teams be able to constantly defend and comeback to the game. Dont let this happen, and dont be affraid to punish a carry for being to close to you, even if its a tank (in this case stun him and walk past him and try to zone the other team carries from the fight while they finish the tank)

Simple!

Go after the CARRIES!

Most people will always be underestimating you and wont expect you to have such an output that you can two shot a carry. But you CAN!

Let me bring it down to you in numbers so you can realize what i'm saying:

In a full build tarick will have around 500 armor and 100ish AD, so let us do the math

A full combo of tarick (full build with 500armor and 100 AD (you will have more)):

E = 200
Auto-Attack (Passive) = 150 + 100 = 250

W = 200 + 150 = 350
Auto-Attack (Passive) = 150 + 100 = 250

R = 350 (for the next 10 SECONDS you gain +70AD)
Auto-Attack (Passive+70 from Ult) = 150 + 100 + 70 = 320

Q = No damage
Auto-Attack (Passive+70) = 320

Now lets sum everything:

200+250+350+250+350+320+320

Which gives you a combo of:

2040

DAMAGE

and i'm not counting the damage that your thornmail and sunfire are doing!

and your passive also gives you a cooldown of 2 seconds per use of auto-attack to all abilities

which means that your DPS turn you into a F****ng monster!

I hope that now you understand everything, tarick is not just a viable choice, but if well played, he will be the king of supports and a perm ban in all game, because he is just to damn strong. Just wait for the lcs to see ;)

So now go and practice everything i just told you, and rush your climb to D1/Challenger before they nerf this