There's a lot of background/hidden data going on in the OS. Restore Points, Hibernation(hiberfil.sys), Virtual Memory/SWAP(pagefile.sys), etc. These can easily eat away precious space on a lower capacity drive. Restore Points and hiberfil.sys can't be moved to another drive without serious hacking to the registry but can easily be disabled. The pagefile.sys can easily be moved to another drive or be spread out through multiple drives.
In the case of SSD drives, it's not a good idea to have files constantly written to, which the above three do, especially the pagefile.sys. This will shorten the life of the SSD.
If you don't use restore or hibernation, disable them. Definitely set the virtual memory to use a non-SSD drive.
For virtual memory, right-click on Computer, select Properties, select Advanced System Settings, select Settings(under Performance), select Advanced, select change. If "Automatically manage paging file size for all drives" is checked, uncheck it and set the settings to your desire. You will need to restart the computer after changing this.
For restore points, right-click on Computer, select Properties, select System Protection, select Configure, then select "Turn off system protection".
For hibernation, select Power Options from the Control Panel, select "Change plan settings" from your currently selected power plan, then select "Change advanced power settings", select Sleep then select Hibernate after and set it to never.
The files for restore will be deleted automatically, while you may need to delete pagefile.sys and hiberfil.sys manually. In order to do this you must have these hidden files viewable. From Control Panel, select Folder Options, select View, then select "Show hidden files, folders and drives". When you're done deleting the two files, change it back.
