Some mods contain scripts to alter files after they have been installed (e.g. [IMG] F1 1993 Season 1.1). This causes CM to detect them as updated by the game and skip their removal.
We can assume that only files with a backup will require this check. There is an edge case of mods installing files that are not present in the current version of the game, but are in a later one. It is very unlikely though.
Some mods contain scripts to alter files after they have been installed (e.g. [IMG] F1 1993 Season 1.1). This causes CM to detect them as updated by the game and skip their removal.
We can assume that only files with a backup will require this check. There is an edge case of mods installing files that are not present in the current version of the game, but are in a later one. It is very unlikely though.