Just about everyone who owns a bong, at some point, thought to put ice in their bong. It sounds like a great idea; it will cool your smoke and make hit more refreshing. I am not so sure if this really is the case though and I think there is good reason to believe that ice in your bong will actually make your smoke session worse.
Lets start with the concept of cooling your smoke. The bong water and the distance the smoke travels inside the bong will sufficiently cool your hit. Adding ice cubes into the mix risks making the smoke go stale prematurely which will make your hit taste really bad. If you hate stale smoke, keep the ice out of your bong.
Using ice cubes also makes your water go bad faster which can ruin the taste of your weed. The ice is pretty cold and as a result some of the smoke that comes into contact with it quickly condenses into some really strong resin. As the ice melts, that resin runs into your bong water and makes your smoke taste worse. I know that changing the water is no big deal but why make extra work for yourself?
Ice is hard on your glass. I know you can buy bongs with ice catchers but I have seen those break too. I don't know about you but if I just dropped $120 dollars on a piece of glass the last thing I want to do is throw some hard ice into it.
This is all just my opinion, of course. If you like ice in your bong, keep on doing what you are doing.