I don't know why anyone in their right mind would become a lead in PHX, and I suspect the overwhelming majority of them do it to be FT for hours and benefits. I have spoken with dozens of leads, and maybe 3 of them actually like being a lead. I cannot recall the last time someone who was already FT ramp decided to become a FT lead, although there are some people who are lead qualified, but they do it just to relieve the boredom and serve as a reminder as to why they aren't accepting a full-time lead position. Plenty of PT people refuse to accept lead positions, while scrounging workbrain for extra hours.
While it is easy to say, "work safe," leads will be dragged into a Manager's office if flights consistantly go out late or they refuse cargo because some Manager thinks there was enough time to load the cargo, even when it is a ground turn and short-staffed. The leads just push themselves instead of relying upon the union to represent them during a write-up. It is a miserable position, and certainly not worth the extra $1/hour for pay, but it is about the full-time hours and lower health insurance costs.
Probably PRez would expound upon these issues regarding the leads, as I think he is lead qualified himself and certainly one of the PHX union representatives.