This is where we get stability on the bike. If your only strength work is on your abdominals, this alone will vastly improve your riding. Strong abdominals are also the key to preserving a healthy back, and are the foundation of strength for a strong rider. Riding with undeveloped abdominals is something like riding a bike with a cracked frame. All the energy gets dissipated in flexion, and doesn't get you down the road.
Squats are also a good exercise to strengthen the torso, if done right.
The weight and torso should rise together as the legs straighten, with the abdominals tight, helping the back muscles to hold the torso rigid. If you can't lift with this style, you are lifting too heavy a weight.