I see value in allowing "read-only" member fields editable only by admins. I've created several fields in my trial of WA related to homeowner information (validated home address and zip code, square footage, home value, date sold, etc.) which I acquire from public government and post office sources. I add these to their data record when I validate a membership request. I would like them to be able to see those values, but not to change them on their own as that could cause confusion and problems with our mailing list. If the member doesn't like something listed, they can always email me and I can fix the problem for them in a controlled fashion.
In other situations, I could see storing member ID numbers, account balances, merit points, raffle ticket numbers, secret santa names, etc. that again would be inappropriate for the members to change themselves, but they would need to view.