having options is the key
i'd rather go through human checkout - but if there is one human checkout lane and 4 overflowing carts already lined up, it forces the issue
Trader Joe's usually has all 8-10 lines open and even when it's 3 carts deep, the lines move fairly quickly bc they know how to scan and bag
otoh whole foods will minimize as much as possible while still looking like they're accommodating (2-3 at best)
Winn Dixie will have one lane open no matter what
i think the rule of thumb should be open another lane when the other lanes get 3 carts deep