You'd choose the 80mm over the 72mm if you have to carry them on your back - out of the car or in the studio it wouldn't matter. Also, many of us are "standardized" on a filter size smaller than the 72 XL's immense 95mm filters. Carrying the 72 would also mean carrying another set of extremely expensive filters - if you use them. But it is a classic and for good reason.
I also find the SS XL series good for sunsets and sunrises because of their flare resistance.