For what applications is sampling a random subset of 7.9e28 out of 8.1e67 possible shuffles not enough?

Heck, why isn't 3.5e17 subsets enough (64 bits / 52 so every shuffle is disjoint)? Why do you need so many? You can't visit 8.1e67 states, so why do you care whether or not some are in principle completely inaccessible?