This functionality was left over from previous versions as stated in the GameMaker help file.
"However, this is a legacy from old GameMaker versions and you should use the == operators for comparing and = for assigning."
It would be good practice for you to use ==
when comparing as that is what it is designed for. Also, if you were to move onto another languages like PHP, using the =
operator would actually initialize the variable in the if statement. This could give you quite a headache if you are in the habit of using the single =
operator.