If you are running version 10.11 you should definitely update to 10.11.1.
If you are running Yosemite 10.10.x, there is no reason not to update. It has some nice features. Here is another explanation on why.
If you are running older versions you can check with me to see if it is recommended for your computer. In most cases it will be.
To see what version you are running click on the little apple on the left of the top tool bar. Select about this Mac.
As always, remember to back up before you upgrade.