As a UK based part time instructor...
(1) Practice Pan is a bloody useful tool for getting a student to take the exercise of making a mayday call or equivalent seriously, because they're suddenly talking to the big scarey outside world of aviation grown ups.
(2) UK D&D cell actively encourage its use, as it provides them with regular training and equipment testing.
(3) I know somebody who got badly lost, close to CAS, solo in an SEP, in marginal visibility. She called ATC, they asked her to change to 121.5, they vectored her to a known and safe location close to her destination. Throughout, the 2-way with D&D was being interrupted by Guard Police telling her and D&D cell off for being on guard!!!!
(4) Damned if I can see why anybody being actively controlled in national airspace needs to be monitoring guard either.
G