From my experience, since I tend to write series more so than single stories...
I wrote the first book of a series and moved on to the second book. Before long, I realized I needed a way to keep track of characters and I am not just talking about the main, or even secondary characters, but all characters who are given a name.
Sometimes a character is shown in one scene in one book and he or she makes an appearance in a second book, or other follow up books. I needed to make sure I got their names right, hair color or any other information so as not to confuse the reader, or an editor...
So I created a Excel spread sheet that list character name, books they appear in and chapters. The spread sheet also allows me to list appearance information or traits I need to remember.
If you have MS office, you already have the ability to make a spread sheet that fits your needs and it cost nothing but your time.
For my single works and short stories, I don't worry about it because I can page back and forth pretty easily...