Originally Posted by NOLAsailing
Almost all foils have two grooves. This is more likely for sail changes than double headsails, I would guess.
Sail changes on a cruising boat don't need two grooves. Take one down, put the other up. Yes you can hoist before dropping but why would you? It's not as if you're against the clock. The most rushed choices you will make cruising is "Should we tack? Nah, let's tack tomorrow"
No, I reckon the second groove is more about twin headsails than sail changes. If you're seriously racing and need to do sail changes, you're probably using a racing foil and not a furler anyway.
There are some sailors who have two identical sails cut that are on the furler together, using both tracks. When sailing on the wind, one lies inside the other. When running downwind, gull them. When furling, furl them together. Sounds like a decent choice.