When an escort offers a service more akin to a 'real' relationship rather than just sex. The escort may go with the payer to dinner / the movies etc and engage in conversation, kissing and so forth, before retiring for sex (as what might occur when dating). Men who indulge in such Girlfriend Experiences with escorts are said to be enjoying The Hobby.
It's get the Girlfriend Experience - I don't need to try to impress her - she'll come out with me on the town and later I get garunteed sex. But she is still a prostitute, it costs me." ... "What's the difference between that and when you were going out with my sister?