Originally Posted by
bikerjp
Will this result in a different length? Longer or shorter? If so, what's the theory? If it's not loose then the chain will be long enough up to the largest cog that will work with the derailleur?
Yes, it will be longer because you're providing the max length chain your RD can handle rather than the minimum length to allow a big/big combo. The small/small method allows you not to worry about chain length if you pop on a larger cassette.
I personally prefer the big/big method of sizing because you absolutely know the length is there plus you don't have more than you need. But if you use that method and don't use a different chain for each cassette, you must size for your largest cassette.