Q:

Is a versioning system or code repository necessary for a single developer?

Why do I need to use a versioning system or repository? I code from scratch by myself and make web code changes along with database changes on reasonably large projects. 

A:

You don't have to do it - but I found out that it makes developing much easier. 
It helped me 

to cut a lot of commented code out of my programs
to get back to an old version (find out why it worked with an older version and doesn't work with the current one)
with my backup strategy

After the learning curve I'm pretty sure you are going to like it

A:

Definitely yes - I have often coded on my own in the past, and a proper versioning system has proved invaluable on countless occasions. 
Also see Good excuses NOT to use version control

