There are lots of ways of varying the sound you get from your bass - your tone knob, eq, overdriving valves in your amp, muting etc.
A pedal can vary the sound more drastically, but is essentially just another way to get the best sound for that piece of music.
I don't tend to use effects myself, but then I'm playing 70's rock type stuff. If I was playing in an electronic outfit, I'd try all sorts of stuff to get different sounds. I think modern music needs to push boundaries, and it makes no sense to restrict yourself to a bass sound that's been a staple since the 50's