Oh, no, that's not a good setting. You've just disabled parallalism server-wide and forced all queries to run single threaded. Having your CPU at 20% is not a good thing, it means that 80% of your server is doing nothing, that's a waste of time and money.
Maxdop 0 is not always good, especially with default cost threshold settings, but you do usually want SQL processing data as fast as it can.
I'd recommend maxdop to 4, cost threshold to 50 and don't think that crippling a server is a good thing to do when it's high on CPU. 100 is too high, but should be fixed with query tuning, not by forcing most of your CPUs to do nothing at all.
Microsoft Certified Master: SQL Server, MVP, M.Sc (Comp Sci)
SQL In The Wild: Discussions on DB performance with occasional diversions into recoverability
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