I think that chain leads CAN be a very useful tool to remind a horse to respect the halter on occasion. I don't think you'll gain much by using one every day though. It's simliar to using a stronger bit, after a while the holes in training show through once they adjust to the new sensations, or it's easy for the handler to "accidentally" yank too hard and over correct when the chain is used all the time.
That being said, some horses that have become pushy and for a short term (as in I don't have time to really work on this now, but I will later) a chain can get a horse's attention. It's also useful if you show sometimes to give a more precise cue, but if your horse is truely respectful and well trained, you don't really need it, either.
I think really a few reminder lessons to back out of your space in his usual halter should suffice (and many people will probably tell you to use a rope halter, but again, that's just using knots /pressure points and isn't much different that the chain concept in my mind..if the horse respects pressure, he will respect a leather or web halter just as well-useful to get attention, but a horse that really understands the "yeild to pressure" won't need the thing rope or knots to be controlled).
If your horse is being pushy, though, I have to be honest..his ground manners are NOT great..he's disrespecting you. Sometimes a few short tugs on the lead will get their attention, sometimes backing them up and out of your space will do it when they get pushy.It may be supplemented by a tap on the shoulder with the end of the lead if the tugs aren't getting through. Just taps, not "whipping". Sometimes more serious lessons need to be taught with more extensive groundwork.
I like to keep my horses respecting my space by turning them AWAY from me when I lead them (most of the time) rather than pulling them into my space..I invade theirs and they yield. Or while I'm grooming, I frequently ask them to step their hindquarters away from me. I just cluck my tongue or nudge their hips over. Again, it's them getting out of my way, keeping them respecting my bubble. If I'm leading them and want to stop, and they keep walking, I immediately back them or turn them or even do a little "micro-lunging" as I call it..if they want to move their feet, I make them move their feet , then ask them to stop again. Just depends on the situation. With some horses I practice by leading them to their feed when I'm done..if the crowd me for the grain, I back them up and make them wait a second..leading forward and backing when they get pushy. This also helps with food aggression in some cases. Then when they are good, I lead them up to the bucket and let them eat, sometimes I'll still back them away while they are eating and immediately back to to the food if they are good. I stay for a while and then take off the halter and walk away.