Yes. It's important to vote IF you think the elections are legitimate and fair. By voting (blank, for yourself, for Mickey Mouse) you say "I didn't like any of the candidates, but I'm ready to accept the result of the majority", thereby giving more legitimacy to whoever is elected.

Not voting can be dissent (I disagree with the process, I don't think it's fair etc) or simply apathy. But in either case it gives less legitimacy to whoever is elected. And that's important: if you don't think it's a fair election/process then you don't want to give the legitimacy.