Does this computed CHECKSUM() index design make sense?
You are right, this is pointless.

Two (of many) reasons that I see it's wrong


it isn't guaranteed unique (CHECKSUM gives int) whereas the GUID is (over the range of GUID). It's a small chance of duplicate but quite possible: like the "birthday problem" somewhat
it's still random order. The main reason IDENTITY is better then GUID for a clustered index is that IDENTITY is monotonically increasing. CHECKSUM(someGUID) is random order too


I'd add a new IDENTITY column, and then start changing dependencies to use this only.