Is there an advantage to delete apps from Launchpad (Hold one app like in iOS) vs from finder?
And why some apps cannot be deleted from Launchpad?
Deleting apps from Launchpad and Applications folder are similar but for an extra step. When you delete from Launchpad, MacOS removes it completely from your system. From Finder(Applications folder), you move it to Trash and have to empty the trash to completely delete the app and generate space out of it.
Those apps which cannot be deleted from LaunchPad (without X) are apps pre-installed by the OS and needed by it or apps that you have installed separately using a DMG file from third party like Google/ Mozilla FF.
Rest apps which can be deleted are apps installed from AppStore.