Check for locally modified files. Without this option, muchsync assumes that files in a maildir are never edited.
checkForModifiedFiles disables certain optimizations so as to make muchsync at least check the timestamp on every file, which will detect modified files at the cost of a longer startup time.
This option is useful if your software regularly modifies the contents of mail files (e.g., because you are running offlineimap with "synclabels = yes").