Recycling is done after assessing a venue and determining that most of the sets have been approached. Sometimes, these go well, but usually, if that many sets have taken place and none have seriously hooked, it is time to move to a new venue and restart the game.
In some ways, pickup is a numbers game, so the more venues a PUA visits and the more sets he opens, the greater the chance that he will find someone he is interested in, who shows interest in return. Even if none of the sets hook in one location, they can be seen as warm-up sets for the next venue.
Source: Little Grasshopper