League of Legends (LoL) Question: Doran's Shield on Supports?

What Vynertje said. It makes you so much tankier and it is essential if you are against all-in combos or if you are against high poke bot. You can still get the support item Ancient Coin/ Nomad's Medallion on your first back, so it won't leave you behind the enemy support. With that item, you can easily tank something like 7 autoattacks more than you would with Ancient Coin, making it a great buy. I take it on supports who are melee/initiating ones ( Leona, Thresh) but I don't always get it on supports like Soraka. Sona is also good with it afaik.

It makes you so much more tanky that if you don't start with it, you have such a big disadvantage over your lane in terms of all-out potential that you're nearly guaranteed to lose your lane.

Doran's Shield is used for trading in early game, it helps you block some AA while you are attacking them.

It depends on your Elo and matchup. You wont face good poke players in bronze and silver division and since your AD could be pushing idiot you really need wards. But if you are Gold and higher you should probably get it against poking rangeds who can have AD or Hybrid pene marks especialy Annie with her crazy range could poke you to low hp and than Flash stun for kill.

I have no idea why would they pick doran shield, beside the obvious effect, in terms of tactic. And I don't believe solo Q should pick doran up, since solo Q tend not to take advantage of such small early stat boost, you're better off with the usual gold income start.