Like all ships Y-wings have their Pros and Cons
Pros- They can take a beating; they can take 8 total hits. That is almost three times what a TIE can take
They are cheap. If you are trying to put more ships in the field, gold squardon is the cheapest the rebels have.
Cons- They only have two attack dice, that is the same as a TIE, but it shure doesn't feel like much compared to the X-wings' three.
They only have 1-agility dice. This can make those 3 shield and 5 hull points dissapear really quickly.
They aren't really that manuverable. For example a hard 3 turn is a red manuver.
I left upgrades until last. Andy they are a huge deal with Y-wings. With two torpedo slots, a droid slot and a turret slot, you can quickly spend any points you saved, by taking the cheaper y-wing. Ion cannon turrets are really a good upgrade and some might conside them a no-brainer for the y-wing. As a fighter-bomer y-wings can also take 2 proton torpedoes.
My recomendation is that you either take the torpedoes or the Ion cannon. I think they just const too much with both.
So how do you use them.
1- 18 points is pretty cheap for 8 hits of damage to soak up. Y-wings are pretty easy to hurt, but they take time to kill. If your 18 point ship drew fire away rom Wedge for 2 turns, then they were points well spent.
2- With an Ion-cannon, I think this is the most popular way. enough has been said about this deployment and I agree with most of what has been said.
3- with 2 proton torpedoes. This is my least favorite way, 8 points is just a lot of points to spend on Upgrades that will be gone by the second turn. But each torpedo has a pretty good chance of killing a TIE and then your opponents numbers advantage might just have evaporated
4- Don't forget Dutch. I love having him feed Wedge target locks.
Putting an end to this distructive conflict and bringing order to the galaxy.