I practically never go on foot. I always use the bike, since I'm lazy and want get to my destination faster, and I guess I just find it kind of fun. I think biking in circles all around the place in my little Pokemon world is just more exiting than running, anyhow, and I like the music it plays, too! <3
It's easier just to run, that's true, but bike is faster. Wait, flying is faster. Um, anyway, you HAD to use bike on certain occasions to complete the game.
I remember on heart gold I forgot all about the bike. It wasn't till near the end I told myself "hang on isn't there supposed to be a bike in this game".