Many creators pile up terabytes of old projects "just in case," with no clear policy. That is both a storage cost and a risk (a client who comes back two years later, a dispute). A simple rule beats an overflowing drive.
The basic rule
Distinguish two things: the delivery (the link your client receives) and your archive (your master copy). The delivery can expire quickly; the archive is managed according to your business.
A common benchmark: keep the master of a project a few months to a year, long enough for a client to reasonably come back. Beyond that, you purge, unless there is a specific agreement.
A backup is not a delivery
Never rely on your delivery tool as a backup. Keep your own copy (ideally in two places) for as long as you judge it useful to hold on to it.
Conversely, don't leave the delivery online forever: it is storage piling up for clients who have already retrieved everything.
Let it expire on the client's side
Announce an expiry date to the client and stick to it. A clear expiry pushes them to download quickly, and frees up your storage.
xFer lets you choose the expiry duration for each delivery and delete a delivery in one click: you control what stays online.
Put it in your contract
The cleanest approach is to write it down: how long you keep the files, and from when the client has to make their own backup. It avoids the "do you still have my photos?" two years later.
In short
Separate delivery and archive, keep your master a few months, let the delivery expire on the client's side, and write your policy into the contract. Less cost, less risk.