Never.
I'm in the All Flock/Flock Raiser plus Free Choice Oyster Shell camp - but I raise (see signature, below) a flock of mixed breeds, genders, and ages.
"Layer Feed" gets you a high calcium feed adequate for average commercial layers with the minimum protein needed to support their typical needs, at a minimum of cost. If you plan to raise just layers, in groups, maintain them on layer till their first molt, then start over - ala high yield commercial management practices, layer is the cheapest way to do it.
I can't take the excess calcium because of my flock composition, but even if I could, the low protein in layer doesn't well support weight gain on any of my dual purpose birds, doesn't help my ducks bulk up (though too much protein can ALSO be bad for them), and isn't expected to help my birds speed thru their first molt. Since I currently plan to keep much of my flock more than a year, that's a consideration for me. Costs an extra $2 per bag, or about $130 year at current consumption.
Really though, it comes down to your flock, your time commitment, and your plans for your flock. Layer isn't good for Roos. Its not good for birds not yet mature. Its not at all helpful during molt. Its not good for weight gain on dual purpose birds. But if none of those are considerations for you, its convenient and cheap.
