No Forced OS X El Capitan Upgrades
There is absolutely no need to install the OS X El Capitan update. Sure, there are exciting new OS X 10.11 features that are coming to your Mac, but Apple will not force you to download the update or to install it.
If you are using an older Mac, traveling or using programs for work or school you may not want to upgrade on day one, and you don't have to.
With any major update it is a good idea to spend time investigating the performance, features and compatibility. After six months of others using the update, you can find a lot of feedback to make an informed decision.