My only experience is speaking with optometrists and listening to presentations about what we can do with an MS degree alongside our OD.
It opens the door for research. You could work for pharmaceutical companies, contact lens companies, etc. Also, in private practice, you can apply to be a part of trials for new products. In these trials, you would recruit current patients or advertise for new patients to take part. From what I understand, this opens new avenues for revenue which are only possible with the MS.
From current students: It's a lot of work. Your course load is already heavy, and this will certainly make it worse. Here at OSU we have a program that allows you to get all, or at least most, of your research out of the way. Your next few years are spent taking your optometry classes and then piling on MS classes on top. Also, during fourth year when boards are done with, everyone will get a slight break. The MS students will be preparing to defend a thesis which means you are busy right up until you graduate.
It's a great program, but it's really suggested for those who want to do research in the future and/or teach. It's not required to teach at most institutions, but it will certainly help you get in the door and put you ahead of other applicants.
