A pre-save is the listener saying yes in advance. They agree once, before the date, and on release day the release is in their library or the link is in their mail, without them having to remember the date.
Why an artist wants them
Release day is one day. What happens in the first hours decides whether a platform's own editors and algorithms pick a release up, and a pre-save moves a listener's attention to that day rather than the week after. It is also the only list an artist can build before there is anything to hear.
What it costs the listener
An authorization to write to their library, or an email address. Both are worth asking for plainly: what lands, when, and nothing else. A pre-save that turns into a mailing list the listener never asked for is the fastest way to lose them.
The link has to survive the day
A pre-save link gets shared weeks before the release and read for months after. An address that only works before the date breaks every post that carries it. One address that asks before the day and plays after it is the whole trick.