I'm not generally a fan of "snap by" for the simple (and rather pathetic) reason that I'm awful at remembering to switch options back to their usual setting once I'm done with the specific-case setting. This leads to all kinds of screwups and frustrations (like switching to offset mode and forgetting it's on).
So what I do instead is to drag clip start points left to the nearest start of a measure, if it's not already there. This way it doesn't matter where the actual content of the clip begins, it always remains in position relative to the measures when I move it. Hope that makes sense.