Strings have huge impact on your playing. Not only in just the sound, but also the feel. I've found that new strings often just
feel better, and really give new life to the instrument. If you've ever gotten tired of your bass or your tone, the easiest and most cost effective way to mix things up is to try a new and different set of strings!
How often you end up changing them is up to you and depends on how much you play, your body chemistry (some people can make a set go dead in a week!

), and your personal preference.