I edited the summary to note that we are not (entirely) blocking system customization.
I haven't worked at a place yet that didn't budget a little time up front for me to get up and running, but it's mainly the feeling of restriction that gets to me. What if the coders get upset enough that they start developing remotely, pushing all their code back and forth over ssh/rsync/whatever, and using their laptops as thin clients? Do you block ssh traffic? Ouch. Lots of coders are brilliant and love subverting restrictions. It seems keeping everything locked up could turn demoralizing for both sides to say nothing of the huge time sink.