My current ride gets locked with a Krypto Evolution 2000 that I got at the LBS for $25 new due to the fact that they'd had it on the shelf for a long time. Some of those locks are pickable with a bic pen, but I've never had any trouble. I also use a Krypto cable lock that I've had for 10 or twelve years to secure the front wheel. I think I'm the only person who does that around here.
Maybe I'm overreacting, but I'm not overenthusiastic about leaving the lock attached to the rack in my absence. I'm only on campus two or three days out of the week, and kind of feel like I should have the lock with me. I also don't know how the campus LEOs treat locks that are left behind. I can find out, but don't recall seeing anything about that in the campus handbook.
However, the weight savings of leaving the lock could be tempting, as well as not having to worry so much about finding space on the frame for a carry bracket.
As much as I care about my bikes and have used locks in the past, some of this feels new to me. I've only been using a dlock since summer. For the longest time, even a purpose-made Krypto cable lock seemed like borderline overkill. Also, few LBSs that I've seen seem to stock too many dlocks. Lots of cables and a few chains.