TekRevue:

Following the path it took with iOS, Apple is preparing to transition macOS to require 64-bit apps. The Mac operating system itself has been 64-bit for years, but has maintained compatibility with 32-bit apps. But that’s going to change soon.

Through the use of a Terminal command, you can configure your Mac to only run 64-bit applications. Any 32-bit apps you have installed on your Mac will still be there, but they’ll simply crash when you try to launch them. The potential issue with enabling 64-bit mode on your Mac is that you (or an otherwise 64-bit app) will end up needing to launch a 32-bit app for whatever reason and it will be unavailable. The good news is that this process is reversible, so if you run into the aforementioned situation, you can always switch back to supporting 32-bit apps.

This is something you might want to do ahead of Apple eventually shutting down access to 32-bit apps. You want to find out what your alternatives are before your forced to.