As a practical matter, many applications span multiple directories, so there is not just one file to delete. If the app, is simple enough, though, sure -- just

As a practical matter, many applications span multiple directories, so there is not just one file to delete. If the app, is simple enough, though, sure -- just replacing the executable can work. Some examples of apps spanning many files and directories are configuration files, cached data, and plugins. For uninstallation, much of that stuff should definitely be deleted; for upgrades, there are occasionally conflicts which installer systems can help to manage (though, often enough, they can only do part of what needs to be done).