If you were carrying them as a spare when touring, the fact that they fold would be useful. Usually though, that they fold will only in-practice mean it costs the mail order company less to post them to you !
They are a bit lighter, as they have kevlar beads rather than steel wire, so e.g. 700x23 Vittoria Rubino Pro (folding) are ca 200g rather than 300g for Vittoria Rubino (non-folding).
A weight saving of 100g isn't a lot, but if you're saving that 100g at any point on the bike, doing it at the wheel rim will make the biggest difference.
But it would be one I'd want on my lightweight race bike and wouldn't be bothered about on my clunky commuter which weighs so much, has beefy wheels, panniers, guards, etc so it won't make that much odds.
From the manufacturers'/retailers' points of view, they're more expensive so presumably more profit, they take up less storage space and are far easier to post to you : no wonder they'd rather you bought them !