Oh baby, that title has so much potential for double entendres.
So anyway. Tight spacing in block layout, from what I can tell, only changes spacing between lines of text. From what I can tell, it still leaves 3-4 lines of text worth of spacing between the last line of one message and the beginning of the other, because it doesn't also change the block padding or spacing between the blocks from what I can tell.
Could tight spacing please make the messages closer in against each other as well, just like in chat? In a roleplay it'll help squeeze more individual posts onto the screen when they're short. Tight spacing should have, like, one or two lines of spacing between the text of two consecutive messages at most.