Visit enough clubs over the years and you are bound to get free dances, outside of the standard specials.
Each club is different. I have been to clubs where you pay a set fee for going to the lap dance area, and I don't mean the $10 fee like they have at Detroit, There was one club in Cleveland years ago where the club made it's cut in high priced drinks and fees. If I recall it cost you $20 for a one time trip with a single dancer or $40 for multiple trips to the VIP. Dances were usually $20 a song, but I often would often have dancers give me one or two free dances after 3 or four songs.
The most common reason I have found is that she doesn't want to be called on stage next. One of my favorites would often offer whoever she was sitting with 3 for 5 dances whenever she heard her name called to stage.
One of my favorites also would give me specials, such as $150 for a half hour in the main room, which was equivalent to about $225 in dances, and as she said more than she made most half hours.
I have also had dancers ask me to head back for a dance, first one on her, for various reasons such as:
Avoiding a certain customer or customers
Hoping I may turn into one of her regulars.
Only needs one more dance to cover tip out.