There are a few different ways to delete an application from your Mac hard drive. Some applications come with an “uninstaller,” and this option should be chosen whenever available. If the application you want to delete does not have an uninstaller you can go into the Finder, right click, and select “Move to Trash.” Make sure the application is not running when you delete it. If you try to delete a running application, you will be prompted to quit. Then empty your Trash.
There are a number of files related to the application, including preference files, that are left even after the application has been deleted. To clean up these files, I recommend App Cleaner in the Mac App Store. You can try it for free, and the Pro version (as of the date of this entry) is $3.99. There is another app by the same name, App Cleaner, available for free on the internet. I have used both, and the one from the App Store is superior.
Using App Cleaner is simple. When you want to uninstall an application, launch App Cleaner. Make sure you grant the app permission to access your Application Folder and user files. Find the application you want to delete in the left column. You will be given the option to delete the application and you will have the option to delete other related files.
Why would you want to leave the files there? First off, the files are usually extremely small. Secondly, you might decide you want to download the application again in the future and it is convenient to have your preferences already saved.
Why would you want to delete the related files? I like to keep my hard drive clean. These extraneous files can build up over time, and storage memory is limited on my SSD hard drive.
I think this comes down to personal choice. If you are looking for a convenient way to delete applications and related files, I highly recommend App Cleaner.