I had a project at a private bank where we couldn't use the internet - we had to turn our phones in when we checked in, had to use their computers on their network, couldn't access the outside internet... we did have access to api documents electronically thankfully. If we wanted to update a library it had to go through a big security review that took weeks.

It slowed work down a lot but was totally fine - the bank was paying us tons of money hourly.