in my opinion, the answer to your question in most cases is "yes." Think about it this way.... Lets take Biggie's "Hypnotize" (95 bpm, 32 beat chorus) and Gold Digger (94 bpm, 4 beat intro) Here is how the biggie chorus goes [1] Biggie Biggie [2] Biggie- [3] Can't you [4] see [5] Sometimes your [6] words just hy[7]pnotize [8] me [9] And I just [10] love your [11] flashy [12] ways [13] This is why I'm [14] broke and [15] you're so pa[16]id-- *repeat for another 16 beats Ok that took FOREVER to do, so you better appreciate this LMAO... So if the kanye song has a 4 beat intro, you start the intro on the 13 beat and then biggie chorus ends and the kanye song begins. Perfect switch. "This is why i'm broke any you're so paid [switch] Now I aint sayin' she's a gold digger..." Now lets say you started it on the 9 beat instead (1 bar early). The crowd would hear "And I just love your flashy ways [illogical switch] Now I ain't sayin' she's a gold digger..." Ya dig? I think your question is kind of like "When writing a story, should you finish one paragraph before starting the next or should you go with the flow?" I mean, you can "go with the flow," but you're going to seriously leave the reader scratching his head. With the above said, there are obviously exceptions to all rules.