Don't Install If You rely on 32 Bit Apps
Apple no longer supports 32-bit apps on macOS Catalina. If you rely on these apps to do your work or for entertainment, you should not update yet. This includes some very popular apps like Aperture, which is an Apple App.
Some users report that older versions of Office are 32-bit and that they need to buy a new version to use it.
Other users report Steam no longer working on macOS Catalina, but you can fix this by downloading the new 64-bit version.
You should take a minute to check for apps that won't work. Here's how to check;
If you see a "No" next to an app, that app will not work on macOS 10.15. Some of the apps are from Apple and are part of macOS. Those should get an update as part of macOS 10.15, but others will not work on Catalina without an update. See if any of these apps are important to your workflow.