My answer is somewhere in the middle. I have to ask, but there's zero chance I'll be told no - it's mainly a formality as we're a company with 50k employees across a broad spectrum of job types (engineering, manufacturing, etc), and the work I do isn't mission critical.
My last job, I could pretty much just tell my team a week or two in advance that I was going to take some time off and then leave. If we ever ran into an issue (like multiple people wanting to leave at the same time), we just worked it out among ourselves.