In case you are interested, it is possible to set your MacBook to automatically disable the Trackpad, whenever a mouse is plugged-in to it.
This setup can help in preventing the possibility of the Trackpad registering unwanted clicks, due to accidental brushing of the palm or fingers, while you are using the mouse.
Disable Trackpad on Mac When the Mouse is Plugged In
The option to disable Trackpad on Mac while it is attached to a mouse is available in the Accessibility settings on your MacBook.
1. Click on Apple Logo in top-menu bar and select System Preferences in the drop-down menu.
2. On System Preferences screen, click on Accessibility.
3. On the next screen, select Mouse & Trackpad in the left side-bar and select Ignore built-in trackpad when mouse or wireless trackpad is present option.
After this, the Trackpad on your MacBook will be Automatically disabled, whenever it detects an external Mouse being plugged-in to it.
When you Unplug the Mouse from your MacBook, the Trackpad will be Automatically enabled and you will be able to use it.