Don't worry Perchies :) this is what a forum is for, learning new things :)
Not really to collect. Just to let them feel whee the "sweet spot" is. You are supposed to position them so the sweet spot is, the poll is only a little bit higher than the withers and for them to stretch into a comfortable contact with the bit.
Side reins are used for lunging to get the horse used to being ridden and bit contact.
I use them first of all to get youngsters used to having some contact on the bit. Ad they get used to that I gradually tighten them up so they learn to give to contact, I can then concentrate on getting them working forward, while they sort out themselves how to carry themselves.
When I start riding they are used to contact and it doesn't freak them out
I would only lunge and line drive in them...some horses don't react well especially the first time, feel something on their heads holding them down and go over backwards. You could use draw reins or bungies when actually ride. My mare is lunged once a week with side reins to help build muscle and teach her contact without having to do the fighting myself (she's kind of a brat ;p)