Basically the TCS only kicks in if the wheels start to spin.
I.e if you pull of very quickly the wheels will start to spin, so the TCS cuts the power to stop it spinning, hence you getaway marginally slower, however it will save your tyres!
If its totally dry then tunring it off will allow the tyres to scrabble slightly but it will grip and pull away faster as the power is not held back at any point.
Unless you make a habit of dropping the clutch and screaming off the lights you wont notice much difference i guess, however in the rain its a must as its spin city if you turn it off lol