The Mac OS Trash is a handy feature: you don't need to worry when you delete any of your files since you can put them back in a couple of clicks.
The problem is that over time Trash grows and takes a significant amount of disk space, especially if you delete big files such as movies, music or high-res photos.
The standard solution for that is to empty your Trash from time to time, but then you don't have this undelete feature any more.
Trash Sort is a simple to use app that will allow you to empty only some of your Trash and keep the rest. You can set criteria such as file name, size and date. For instance, you can delete your *.mov files - the ones that are taking the most space.
NOTE: To buy Trash Sort via the App Store an Apple account is required.