This will depend on MANY things, including but not limited to:
- local custom
- office politics
- special concerns (I can't think of any, but more in this later)
- utilization of the rack
- your feelings on the matter
- type of lock
Local custom is important. In some areas it's horridly rude; in others it's common. Does the parking complex for cars have assigned spots? If so then the lock on the rack is probably just an extension of that.
Office politics play a big role. Does the lock belong to the owner of the building and buyer of the rack? Because if it does, you're out of luck. It doesn't matter if it's rude or not - you're not going to win this fight. Or does it belong to an employee who has made a stink in the past and the proposed solution to some problem was to leave the lock?
I can't really think of any special concerns that would affect this, but I do have a similar example from when I used to leave the lock on the lockers at the company gym. Essentially, I was told it was rude to leave the lock on the lockers at the company gym. But this was an arrangement I made with management because I would frequently work half a shift, work out, shower, return to work the other half of the shift, and leaving smelly work out clothes (and I can be smelly) in the locker room was better then stinking up the office. And, because my time around the campus was extensive, in the morning it was better to deposit the clothes in the locker then to have the gym bag around my desk.
If the rack is under utilized, and you know it's going to stay that way, it's a much smaller issue. For example, a 25-bike rack with an office size of 20 people and only 5 of them bike. Then it's not rude at all.
This is tricky. But make sure you have a legitimate reason to be upset. Often we bikers think of ourselves as "last on the list". We see it as a treat to have a bike lane that's clean and free of debris. Make sure you're looking at this issue objectively.
I would add that the type of lock is important. Our local bike shop has around ten types of lock, ranging from a simple cable with built in lock weighing around a pound to massive, complicated bar and cable "systems" that weigh closer to 25 pounds. Their most popular option is a 5 pound cable and U lock combo. Either way, I would not want to carry around some of their heavier locks.