I'll give you
my technical definition, if I wasn't clear:
"True" sublimation = solid ---> gas ---> solid (with no liquid phases either on heating or cooling).
"Efficient" relates to the degree of separation of compounds/enantiomers/whatever.
Entrainer sublimation is
the most efficient means of purification - there's a good chapter in a book Chemical Separations by Clifton E. Meloan - with numbers and equations too!
In practical application, the degree of separation is increased by melting the solid first - so that this is then not a "true" sublimation. But only to a pedant!
"Ultra-purification" of metals etc. is typically done using entrainer sublimation - because of its "efficiency".
I believe that the original question was a homework question - and thankfully I don't have to answer it!
Why has someone taken a mole snack?! Is it to discourage contributions or something??? I can take a hint! Bye!