Don't Install if You Use an Old Mac
If you are using an older Mac, you should wait to install macOS Sierra. We consider any mac older than 2013 an old Mac for these purposes. That's where Apple starts to cutoff features and it's also where you can start to see some issues with performance.
It's a great idea to wait for others to test macOS Sierra on the same Mac you have before you jump in and try out the upgrade with your computer and your files. If you have a very old Mac and you haven't done a clean install lately you may want to perform a clean macOS Sierra installation to get a fresh start for your computer.
Check on forums, on Facebook and Twitter to see how your specific MacBook, MacBook Pro, MacBook Air, Mac Mini or iMac handles macOS Sierra.
Now that the update has been out for about a month, you can easily find macOS Sierra reviews from users with similar computers so you can make the right call.