However if you're creating music to sell or shop in the industry then YES! Here is what a master clock is:
Every interface, or unit that converts digital to audio will have a clock of it's own. For example, your digital
mic pre such as the focus rite liquid channel or the Motu 828 will both have these protruding silver connectors in the back where they allow you to connect a external word clock so you can use a clock that is not the one that is already being used inside of it. The clocks already present in these units are descent at best. What its job is is to sync the audio, reverbs, etc so that it lines up and gives you back what you put into it. A dedicated word clock does nothing but sync. This creates a sound that is noticeable in any studio that does not have a word clock. You'll find that your high end is broader and your low end has become more round. As a result your overall sound is tighter and fits more into the professional world.
Some people have never upgraded to a master clock and have gotten placements and made money. Its not a must have. At the end of the day it's not the gear it's the song. The studio I work @ has upgraded and I've noticed the difference. I'm blown away at how my mixes and production is turning out. On some project I'm going back and re-bouncing some songs. It's worth looking into.