Guess I'm gonna dip into my old Fighter days.
When an aircraft becomes airborne, the wheels are spinning at a considerable rate. Allowing them to continue spinning as they enter the wheel well can have some pretty catastrophic results.
Many aircraft use an anti spin system to stop the wheels from spinning before entering the well. Basically what happens is once gear is selected "up" AND the squat switch is released (or activated depending on the system), hydraulic pressure is applied to the brake system automatically to stop the wheels from spinning, prior to them entering the wheel well. Once "up and locked" the pressure is removed.
Conversly when landing, if the pilot is applying pressure to the brakes before touchdown, damage and/or very premature wear to the tire can result. (due to the fact that the wheel is unable to spin at touchdown). In order to prevent this, many aircraft have an "anti-skid" type system which won't allow hydraulic pressure to act on the brake system until the wheel hits a set rotational speed. (basically allowing the wheel to come up to speed once on the ground, so great chunks of tire aren't ripped off at touch down).
Now, there are other methods used ( REN pointed one out) as well, but these systems I have described are fairly common for larger and/or higher performance aircraft.
Cheers,
RTR