I’ve always been a huge fan of Local History. It’s one of those pieces of standard Eclipse functionality that adds great power to Domino Designer. And because it’s standard Eclipse functionality it’s something developers find out about over time.
So a bit of background quickly. Local History allows you to retrieve previous saves of design elements made on the current PC. Because it’s native Eclipse, it’s only available in the standard Eclipse editors and the design elements that use them, so XPages, Custom Controls, Java libraries etc.
Also, because it’s standard Eclipse functionality, preferences can also be set. You will find them under General > Workspace > Local History. You can set the number of days to keep local history, maximum entries per file and maximum file size. Because you’re using Domino Designer extensively and regularly save, you’ll probably want to increase them.