By default, we assume you'll want the backlight on all the time. However, you may want to PWM control or otherwise turn off the LED backlight to save power. You can do this with a simple hack. On the back, look for the backlight jumper.
On the resistive TFT touch shield
Solder the jumper labeled Pin 3. Then you can use Digital 3 to control the backlight.
On the capacitive TFT touch shield
Solder the jumper labeled Pin 5. Then you can use Digital 5 to control the backlight.
Advanced users may want to get an interrupt on a pin (or even, just test a pin rather than do a full SPI query) when the touchscreen is pressed. You can do that by jumpering the #7 solder jumper labeled TS int. We didn't want it to connect to #2 or #3 since those are the Leonardo I2C pins. You can use pin change interrupts to get an interrupt callback on #7. Or, with a little blue wire, advanced users can connect a wire from the TS interrupt pad to any pin they choose. We find that querying/polling the chip is fast enough for most beginner Arduino projects!