Currently accounts can only be locked indefinitely, since the feature to globally block accounts without locking them isn't going to be implemented anytime soon (where users would at least have an option to theoretically appeal a local block), there might as well be an option that allows global accounts to only be temporarily locked, with most forms of disruption local admins usually begin with 24 hour or 48 hour blocks to show that they're serious, there is absolutely no reason why indefinite global banning should be the default.
Most of the usage for lock is for spammer, vandalism only accounts, or returning trolls. While the ability to set ending date is a good feature per se, our current practice will probably remain default-to-infinity.
I don't know about other projects but on enwiki we usually indef block accounts engaging in behaviour that gets accounts locked. And when an expiry is applied anyway, what typically happens is that the account is gone completely after the block has expired or that the misbehaviour continues, requiring more work at cleaning it up/more readers seeing vandalized or spammy content.