Potentially, yes. It's not a hard and fast rule by any means. But the more different the cabs, the more likely you are to get into phase issues and other related acoustic problems that
could compromise your overall sound.
A good acoustic engineer - who has access to data concerning
all the possible factors - could likely finesse the issue with you, so that you could use very dissimilar cabs, and still yield a great tone. But the average layperson - including the players - simply lack that kind of knowledge and expertise. So for them, it's generally simpler and easier to keep the cab dissimilarity to a minimum...
MM
