well taking a shot in the dark...
it takes several thousand scrip to pick up all the poses...a woman might have the poses available to ensure she has full choice of options, since not all male partners may have had the scipr to purchase yet. Limiting the play to Premiums isn't fool proof, but you might have a better chance of matching up with someone who knows what they are doing, other reasons might be visually enhanced with an Av that is not so generic..., capacity to gift...and quite frankly, because of the investment is not so prone to just disappear..but I am just speculating Apollo... a woman should give her reasons.. of course the obvious 3some capability.
I have often been asked by noobs which pose to pick up...and like you I made the comment..."why?" most guys who have been for any length of time have their own...I tell them just focus on the personal wear and appearance when they start... if they want a pose choose a favorite to ensure they have access to it.
As to a guy limiting it,,,mmm...I know I prefer Premium partners only because they are more likely to know how to play the game...use some language skills. Some guys may be hooked on the visual images though too...specific clothing wear (fetish)