Actually yes it does matter. If everyone picks randomly, we know our targets have come from a trustworthy source. We're not saying it guarantees catching a mafia every time because clearly it doesn't. What it does do is make sure that our next target is coming from somewhere devoid of outside influence.
If you pick your target based on suspicions, you could be wrong. You can interpret things wrong and get a townie lynched because of your own bias which is worse than getting a townie lynched based on cold, random numbers. If you've based your vote on your own bias and get a townie lynched, that's on you. You can then dwell on what might have happened if you had picked randomly.