There is not advantage of doing it on a regular basis or at all to Run the computer.
The advantage of having a Bootable external drive is IF your internal drive fails or get corrupted you have a way to start the computer and to do maintenance on it. and that you have a backup of your programs and files. you should also have a second external to do Time Machine back ups on.
Starting up from a clone is usually done if there is a problem starting up from the Main Drive or as a matter of trouble shooting. I'm not sure there are any advantages to the average user to boot up into the clone.