OP. I used to lock my bike exactly like that when I attended class at a local community college. No problem for months. Then one night the bike was gone, the cable cut.

The campus security told me I should use the U type locks. He said that right now the thieves were passing them up because it was so easy to cut the cable type locks. He also showed me the video footage. I had felt safe because there were security cameras all over the campus. After dark the cameras couldn't see squat at the bike rack.

With my new bike I started using both a u-lock and a cable lock. The u-lock covered the frame and back wheel. The cable covered the frame and front wheel. I just took my chances on the saddle as well.