This little procedure just saved me over 20 gigs (yes, this is right, gigs!!) of space on my hard drive. It has to do with how Lightroom updates. Read on or watch the video.
Here is something I was quite surprised to realize. With each catalog, you can set how long it would keep 1:1 previews. I usually set this for a month.
Keeping 1:1 previews is quite useful as it really speeds up using the develop module. Sadly, 1:1 previews do take quite a bit of space. This is why Lightroom has a feature that allows you to automatically delete those previews after a while. For me this duration is set for one month. After one month Lightroom will automatically delete those previews. This is a great balance between usability and space.