If you look at it from a perspective of thermal resistance, you would have a higher resistance with a single block.
Is it relevant?
Well, most drives will work well without water cooling, which brings up the question: why watercool it at all?
It's not necessary, and just like the rest of our watercooling ventures, it's not worth the money (not cost efficient).
So if you only want to cool only one side, go for it.
