This stat becomes REALLY useless when you multi-table. PokerTracker keeps track of each table as an individual session.

Therefore, I could sit and play four tables for two hours...lose $1 on three, win 103 bucks on the other one. I've had a $100 winning session, and I would call it one session. Pokertracker says I played four sessions and lost three of them.

On a side note, on the sessions tab click "show true win rate" and you can see your actual hourly rate. Period.