Is it wise to turn off the iPad completely if I don't use it during the day?
The total life of the iPad's battery is going to be affected by the temperature you keep the battery at and the number of discharge-charge cycles it goes through.

Turning off the iPad will cause the battery to drain more slowly than leaving it in standby mode. But the battery will still be draining when the device is "powered off" as there's circuitry enabled to detect you pressing the power button to turn it back on.

I'm not sure how long an iPad that's off will hold its charge vs. one that is simply sitting in standby mode. I can't imagine the marginal gain in battery life is worth the hassle of waiting for it to power up every time you want to use it.