Why do brain MRIs

Hello all:
I'ma regular lurker and have learned so much from this site. I have a question about the oft-cited advice on the site to insist on regular brain mri's for stage iv.

I presume such regularity would allow one to catch the mets earlier. What is the treatment advantage? Is there an actual survival benefit?

My oncologist is not a huge fan of lots of scanning -- and frankly given how incredibly stressful it is I don't enjoy it much myself. My doc would probably be more inclined not to scan without symptoms. But I know that my doc would consider otherwise if I had other information.

Thanks in advance for any insights anyone can share.