How is getting a MRI "better safe than sorry?

MRIs do not necessarily correlate to symptoms, sometimes it does. You can be feeling fine and the MRI might show new or more lesions - you could be having new or increasing symptoms and the MRI does not show changes from your last one.

It's always best to treat the patient NOT the MRI.

I had a MRI during the diagnostic process in 1985 and never had another MRI until 2005. The only thing the 2005 MRI did was confirm my clinical diagnosis, which was NEVER in doubt, from 1985. At this time I have not had a MRI since the one in 2005.

I believe most neuro's do MRIs once a year when you are on one of the DMDs, at least my neuro does.