Hot/humid climate 3a (South Carolina)..crawlspace w/moisture barrier, unfinished 2nd floor (plan to finish 1450sqft), & it’s a modular home.

I’m sorry to beat a dead horse.  I would like to know if spray foaming the perimeter of a rim/band joist would be as advantageous from an air sealing perspective as insulating the entire area(s) of each rim joist w/spray/rigid foam.

Why not just do the perimeter(s)?  How does air pass through wood if it has no cracks to pass through?

Thank you for the articles and comments—I am learning a lot here.