ares v125.1 is an emergency point release to fix a major performance issue that has exclusively impacted Windows users. If you're a Windows users, you probably want to update.
Additionally, it fixes some minor crash issues, implements the GTROM mapper (used by some NES homebrew) and fixes an issue where some roms could not be loaded from a .zip file, these changes would usually have waited until v126, but since they have already been completed, it didn't make sense to hold them back.