Dating files and keeping whole copies creates more baggage. Lots of files and sometimes confusing to find the latest one.
You are open to changing a previous version thereby contaminating the version timeline which can be very bad if you want to go back and figure out the evolution of the document.
It takes more space since the version control system may be applying diff pages to subsequent versions.
If you have files you don't know whether to create a new copy and then work on it or to modify the latest one. Version control has a clear process of checkin when you want to freeze the content in a time stamp.
Version control allows you to make tags and releases and maintain them together with the work files. This helps maintain a pristine copy of the release or tag accessible anytime.