Over time new Snap updates will use up hard drive space so the user must remove the previous Snap updates.
The default setting is to retain just 2. (3 on Ubuntu Core)
So you should only ever have no more than 2 or 3 at any time.

You can periodically run a simple command/script to remove older unused versions.
The point of the revisioning system is to allow new updates to come, but still have an easy fallback if they're broken.

You can also put a hold on snaps to never update if you want.