The only reason you would want to turn it off in good weather is if you want to do block-long smoky burnouts, or you enjoy deliberate Dukes-of-Hazzard style oversteer on your rear-wheel-drive car. If that’s not your thang, then leave it on. It’s a watchdog that doesn’t do anything unless it senses one or more wheels starting to slip; it costs nothing to have that watchdog paying attention. If you turn it off, the wheel speed sensors are still active (for the ABS system); the computer is still paying attention, it just won’t bother to intervene when your wheels start slipping.
The wheel speed sensors probably won’t be the only ones used by the TCS. There are probably yaw and steering angle sensors too, which will not be used by the ABS. It’s not as though any of those sensors will “burn out” or something if left on, though.
The only not-fun-related downside to leaving TCS on all the time is that you will get slightly increased brake wear, and not even enough to notice.
I would think this is only an issue if you are in the habit of regularly applying enough throttle to develop wheel spin (requiring intervention by the TCS). In good weather, this is rarely a problem unless you’re a leadfoot.
Well, it’s not going to be an issue even then. But most traction control systems will apply the brakes even during “normal” driving when it’s not actually necessary in order to avoid larger inputs later on.
Back when I was a hot-rodder my comment to anybody burning out was always: “Goof! He skimped on his tire budget!”
It’s a lot more difficult to complete hand brake drifts around the corners on snowy roads if it’s on… 
If you choose to drive like a sane person there’s no down side to leaving it on, especially in good driving conditions.
There is no cost to having TC on in normal driving conditions unless you drive like a hooligan. It might even cost you your life if you turn it off all the time. It is a safety device. The only time I can think of to turn it off is to take your hooliganism to a new level. Or on a track where you know the conditions already. Then you if you are a really good track driver, you could actually do better lap times without it. But since you are asking about it, I think it’s safe to assume you aren’t.
I seem to remember back when Juan Pablo Montoya (and TC) was in F1, he was quoted as saying something like he could beat TC over a lap or two, but not for the whole race.