Hello mbehr22,
You've come to a great place for help with managing iMessages on your Mac. To confirm, are you wanting your Messages to remain accessible and viewable on your Mac? If so, you may notice Messages utilizing storage space on your Mac. If you're not wanting iMessages to appear on the Mac at all, you can disable Messages in iCloud via the steps listed below.
- "Open Messages.
- In the menu bar, choose Messages > Preferences.
- Click iMessage.
- Select the tickbox next to Enable Messages in iCloud."
Use Messages in iCloud
After disabling you can delete the messages on you Mac via the steps in the article below. Deleting the message threads on your Mac will not remove the message threads in iCloud or on your other devices when Messages in iCloud has been disabled.
Delete messages and conversations in Messages on Mac - Apple Support
If you'd like to learn more about other options for managing the storage on your Mac, the article below provides great information.
Free up storage space on your Mac
Have a great day!