I agree with the other gents, it's a bit of marketing tactic the ladies use. Kind of like "low volume", "upscale", and "elite companion" it looks good on a resume - but I don't know how much actual value it has.
I try to be very respectful of the provider's time, but if she encourages me to stay and chat a bit afterwards I always appreciate that. Getting to know your partner a bit is a nice perk of the hobby. But I certainly don't expect it for free.
I do think there is a bit of an art to this "extra time" on both sides. If a gent is asking questions about setting up the next session - such as things she likes, if she's into something (fetish, role play, or doubles for example) it's likely in her best interest not to push the gent out the door too quickly. I would say discussing future business is an important reason to possibly allow a gent to stay a few minutes over.
A good provider (and businesswoman) should always have her antennae up to pick up on clues that there will be a next time, what items are of interest to the gent, and any possible things she can do to facilitate that next encounter (such as helping get a doubles session arranged).
Of course it's up to us gentleman to not take advantage of a lady's kindness and hospitality if she does offer us some "extra time" and don't kick our sorry butts out the door. Like they have every right to. LOL