I like to ride my mount but I also like to show off my pet too. So why not be able to do both... at the same time! I know that some pets are to big to fit on most mounts (the brainy assistant) so they would simply be unable to unless the wizard had a big mount. (the t-rex mount) Most pets like dragons and crown shop pets would be able to sit on the back of the mount with you. Pets with wings could fly next to you as you ride your mount.
