Around 10 years ago, I had an brain MRI with contrast. I specifically googled it and found a paper saying it builds up in the brain. I asked the MRI specialist about it, she was surprised I knew this and said she was familiar with the research. She mentioned that her professor also knew about it, but that the paper had other motivations, some conflict of interest, and that I shouldn't be worried. FFS.
Contrast isn't always necessary. Am not a doctor, but I have MS and get them regularly.
I've only had a couple with contrast. My understanding is that contrast highlights abnormal stuff and some tissue sorts more than without contrast. Specifically, they use it in MS to get a better look at an active lesion in the brain. You can still see the lesion without the contrast, though, so most of the MRIs are taken without contrast and then another with contrast if necessary. They have known about various side effects of contrast for some years (allergies, etc).
