Basically stall speed is what you get when you put your foot on the brake, and push on the gas until either the tires spin or it wont rev any higher.
Low stall slips less, and engages nearly right off idle. But, if you are trying to accelerate faster, you want to be in the motors powerband sooner. So a higher stall will put you there.
In a turbo application, it lets you make more boost (higher rpm= increased exhaust=higher boost) and leave from a dead stop with more power.
Converters, just like gears, cams, timing, etc, are dependant on the application.
Stall speed is also dependant on torque. If you take a converter that stalls at 2000 rpm for a stock 350, and put it behind a race built motor, it will stall higher. Hence the need to match the converter to your motor.
The trade off in going for higher stall, is increased trans temp (because the converter slips more), and decreases gas mileage, due to the slippage. But, with a trans cooler to help temps, and a locking clutch conveter (locks input & ouput together at highway speeds) those trade offs become less of a concern.
Hope that helps, man!
