My best guess... Breaking glass may be a symbol of his shattered soul. Angel can never be fully human and the pain from all the chaos he created with Darla.
I don't think it's symbolism, I think it's just really cool to have a non-sparkaly vampire smashing through windows. Edward never does that in twlight, another reason Angel is way cooler.
joss whedon once said that we dust vampires because we can't have the slayer using her strength to dig graves every week (or day) plus it looks really cool!!!
i am assuming having angel smash though windows in sooooooo many episodes adds some cool effects for not only the fans to enjoy but because it looks really cool!!
