It is strictly not necessary to change the prefix of each photo, as I follow a well-defined method of arranging the photos as per decade > year > month as well as decade > year > month and event.
But there is that random chance that I may want to create an album over multiple years. For this purpose, I will need to put many photos into one directory. When viewed as per their file names (which is the sort order I use commonly), all photos will appear mixed. Unless the file view is arranged by date, the photos will not appear in the proper sequence. By using a well-defined prefix with each file, it will ensure that photos appear in the same sequence when displayed by filename or by timestamp.
To rename files, I use a Windows batch script