I have a yearing so I don't use bridles yet...umm I normaly just use a halter and a lunging rain or a halter with a circingle on and the halter attached to that....i normaly lung her every night for about 10-15 mins but atm she has moved into a new paddock so I have to let her settle in there before I start again.
Umm I lung because I think that it helps with body building, rythem, impulsion, tempo, collection which is pretty much everything I have just said lol and I think it also helps with flexsion.
Have you tried free lung her? That's what I did for about year until my horses turned 2.5 (one) and 3 (other one). Actually, they both don't like lunging much (prefer free lunging), however since they learned all commands on free lunch, they do obey them on lunge line as well.
I lunged my paint stallion when he was younger. Depending on the situation, I used regular halter and lunge line, bridle and lunge line, sursingle and side reins, or free lunging. Early on, I lunged at times to help him burn some energy/get exercise. I also lunged to help him develop his form and learn how to balance (not lean) on the bit (although, leanning on the bit has been an issue of his until quite recently). I now hardly ever lunge him because we are so busy working on various other, more specific skills. He is now five, and I ride him between 1 and 3 hours almost every day - he has no need for additional exercise or to burn energy. The skills we are now working on are often too specific for lunging. Sometimes for fun, I free lunge still, because I like to see him move :)
For our lesson horses (who are only used for lessons and occasional rides), I like to free lunge or lunge on a line with a halter just to make sure that they are not feeling too frisky before kids work with them :)