Logic Pro X introduces a new Project file format, with the '.logicx' file extension, which is incompatible with the previous '.logic' file format.

One of the benefits of the new file format is that more data can be saved within the project file bundle itself. For example, when you save a Project, the assets for that Project can now be saved within the project file bundle so that everything is contained in a single file. (You can also still save a Project as a folder, just like in previous versions.) Additionally, Projects can now contain alternate versions. So if you're the sort of person who saves successive Project files as v1, v2, v3 and so on, you could now save (and recall) these incremental versions as Project Alternatives within a single Project file. You can also later rename and remove older versions via the new Edit Alternative window.

Another improvement is that Logic Pro X now has a proper auto-save implementation that works in the background, so you don't have to worry about losing information if something bad happens and you've forgetten to save. I only had one crash after updating to 10.0.1 (10.0 had a few stability issues), and Logic prompted me immediately upon restarting to ask if I wanted to use the auto-save version or my last saved version. Fortunately, auto-save seemed to have kicked in right before the crash, and nothing was lost. This is obviously a big improvement upon Logic Pro 9.