Compiling On Save

To compile metadata on save be sure mm_compile_on_save is set to true

Compile API

By default, MavensMate will attempt to compile Apex/Visualforce metadata with the Tooling API. If you prefer to use the Metadata API to compile Apex metadata, you can set your mm_compile_with_tooling_api setting to false.

Conflicts

If your local Apex/Visualforce metadata is out of sync with the server copy, MavensMate will prompt you with a notification at which point you are presented with a server diff. To turn conflict checking off, set mm_compile_check_conflicts to false. To skip conflict checking for a specific compile, use the MavensMate > Force Save Active File command.