Some strings can be used to throw people off. For example if you're poking with 21 or 32 and your opponent is taking their turn after you can finish the string and hope to catch them sometimes. Given that from memory 21222 and 3212 aren't particularly safe on block however this is iffy at best. Some enders just aren't worth using pretty much at all. B231 is a great string for example that is safe enough, hit-confirm-able and has a surprise FB to catch people with but finishing with B231434 is by comparison not very good at all.