Rick Steves book mentions SBB has a service where we can send bags ahead to another station and pick it up after 3 days (1 franc per day if it waits longer). I am thinking of using this to transport a big bag to reduce the stuff we carry. Send it from Lugano to Interlaken (pick it up after 7 days) and send it back from Interlaken to Lugano (pick up after 6 days).
Are there any restrictions on this service? E.g Is it allowed even if the station is not the next on my journey? Is it allowed even if I have not pre-purchased all my tickets (may want to keep it flexible following Rick Steves advice since online purchases can't be refunded)?