I just successfully reclaimed space on my SSD today on my MacBook Pro, but it was heart in mouth stuff..... here are 2 key points I learned from my experience.
1. Be patient. There should be a warning but there isn't, that the reclaiming of space takes lots of TIME! There should be a warning that it could take 45 minutes to an hour.
2. Be patient again! The counter for the process of reclaiming space was stuck on 40% for me for about half an hour..... it seemed like absolutely no progress was being made. I almost turned off my computer a couple of times, but thankfully I didn't as I read of possible corruption issues as per this post! Therefore, keep your computer plugged in and just let it do its work.
3. Back up before you go through this process. In hindsight, and there should also be a warning to backup, and there was early mention that Parallels "recommends" backing up before reclaiming space, but there isn't! It's just a clean button without warning.
Hopefully my experience helps somone.