Sometimes the boss wants to know who changed something on the website or changes their mind several times on where a button should go, what color something is, or whether or not a page should show up at all. Is there a simple way for a small 2-3 person web team to keep track of these constant changes?
Also, Git and Mercurial allow you to have 1 solution for all your developers and handles branching and merging very easily. It will also show who changed what, when they changed it, etc.
You might consider trying a hosted version control solution like Beanstalk just to get the feel of it. It is very easy to set up and free to try out.
(I don't work for Beanstalk. There are other similar services).
The simplest answer is basically what you hinted at in the tags: Use a source control system. If you are using a CMS for the website that may be able to track the changes for you (i.e. have a source control system built in).
Otherwise you can simply install a system yourself.
Given the size of your team I would go for Mercurial because it has all the modern features and is very easy to setup and use. If you guys work under Windows I'ld simply install TortoiseHG and read this tutorial by Joel Spolsky.