Do you use a lot of older Mac apps or custom apps? If they are 32-bit apps, they will not run on macOS 10.15. Apple started warning users on macOS Mojave, so you likely know if you are using a 32-bit app, but if you aren't sure it is a good idea to check.
Aperture for example is an Apple app that will not work on the new version of macOS. You should take a minute to check for apps that won't work. Here's how to check;
- Hold the option key and click on the Apple Logo in the upper left.
- Click on System Information.
- Scroll down to Software and Choose Applications.
- Click on the 64-bit menu option to sort by it.
If you see a "No" 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.