Version control systems provide you with three important
capabilities:
Reversibility: the ability to back up to a previous state if you
discover that some modification you did was a mistake or a bad idea.
Concurrency: the ability to have many people modifying the same
collection of files knowing that conflicting modifications can be
detected and resolved.
History: the ability to attach historical data to your data,
such as explanatory comments about the intention behind each change.
Even for a programmer working solo, change histories are an important
aid to memory; for a multi-person project, they are a vitally
important form of communication among developers.