...if you are visiting Havana, and you want to see the salsa/timba bands.
Gabriel wrote this post in November of 09, so things may have changed somewhat (they always do). Many of the bands go on national or international tours from time to time.
If the bigger bands (Los Van Van, Pupy Pedroso, La Charanga Habanera) are in town, they often play these same venues on the weekends.
I recommend the matinees, because they are cheaper, and therefore the rooms tend to fill up with Cuban people. Which is half the fun.