I think you guys are confusing terms. The choice you have to make is not between a loose footed main and a shelf footed main. The choice is between a mainsail with an attached foot and and one with a loose foot. A shelf foot is an option that you can get with either of those types of sail.
A sail with a standard, attached foot has a shape that's good for most purposes, but a shelf foot allows you to shape the mainsail with a very deep pocket along the foot, which generates more power in light air. As the boat's speed increases, you adjust the outhaul to gradually decrease the depth of the pocket.
Because the shelf foot is used in light air, most sailors won't feel or perceive a difference in the boat's speed or the sail's power, unless you're near another boat, where you can compare your speed.
I raced and cruised with a shelf footed mainsail for many years and loved it, but, it works best with a little more active trimming than a mainsail without a shelf foot. I can't think of any reason why either a racer or cruiser wouldn't want a shelf foot, but most people don't have them. I suspect it's just because most people don't know about them. If you get a shelf foot, I'd recommend you also get a flattening reef, for those occasions when you have a lot of wind and need to flatten the sail to the max. The flattening reef is especially useful with an attached footed mainsail. It might not be as useful with a loose footed sail. If you're going to buy a loose footed sail, I'd suggest you ask your sailmaker's opinion on that question.