I have been helping riders with their horses for many years now and have developed techniques through my own experience which I have then seen other professional riders using, and I have taken tips and ideas from others as well.
It is very likely if you come to one of my pole clinics you will see layouts I may have shared on Facebook from someone else's page.
Using poles on the floor we are helping the horse to develop proprioception, making sure they know where their feet are and what they need to do with them.
Working with trot poles we can alter distances to encourage the horse to lengthen and shorten it's stride. A really great way of helping a young or inexperienced horse learn how to produce medium trot. It also gives the rider a great feel for the difference in stride length.
Raising trot poles off the ground helps to activate the hocks and strengthen the hindquarters, really giving the rider a feel off the moment of suspension that is part of the trot sequence.
Walk poles I first used to help with a horse who liked to fall onto the forehand and rushed over trot poles. Slowing down to walk made the horse think and start to relax. Raising the walk poles helped lift the shoulders & keep them up.
I like to use raised walk poles to practice trot, walk, trot transitions, and simple changes (canter, walk, canter) as the walk has to be properly established, and the shoulders stay up and the transitions are all uphill.
Canter poles can be a challenge to set out. Often with a straight line of canter poles riders find it hard to keep the horse in a regular rhythm & stride length.
I have found poles in a slight fan on a curved line help more as the horse shows less tendency to lengthen and rush, maybe it also helps that the rider is having to think about the line they are riding through the poles.