That's a common practice, but very foolish. If your employee is at all trustworthy they don't need to have their access revoked (and if they aren't trustworthy they'll just do the damage before they tell you they are leaving). So your org is robbing themselves of employee time without any actual benefit.
You're preaching to the choir here. The most depressing thing is that people leave, like a forest fire, behind echoes of their impacts but we never really get to give them their flowers. The turnover is so rote and frequent that when the best guy in the team leaves, it's not only just a 'I'm so proud to have ... Thank you guys...' email or slack message, but everyone else is like 'Just Another Monday in Corpo Hell.'