Does it make sense for my colonists to wear smokepop belts or should I avoid making them? Do they help much in combat? I could see them helping if I was attacking a item stash or outpost with turrets, but do they help for base defense?
Imo shields are a better choice, if you have access to them. Smokepop belts might be useful if you have multiple melees stacked together that need cover in an open field, but I prefer not to have that kind of situation anyway...
I like to use them on my gunners. It's not a necessity but it sure does come in handy. Helped prevent some nasty wounds in a couple mech raids. I would definitely have gear and weapons prioritized before making them.
They help your ranged guys out a bit - A layer of defense on top of all the other layers of defense a good fortification can provide melee guys can make them nearly unhittable. For melee you're better off with shield belts, but for ranged guys smokepop belts are nice.
If you use smokebelts on shooter and it pops, does it affect your own man too? Should be i think.
If they are in a bunker and nobody can see something.
Yes, smokepop belts also decrease the accuracy of your own shooters.