Not really. You almost always would need to resize or somewhat edit them anyway. And if you care about performance, you would want them in a sprite sheet, so you need to recombine them.

Having them in a single document is much more convenient than having a few hundred open documents in photoshop.

That is relevant for the web. Really though, I think fonts are the way to go for web icons. Crisp at any resolution and CSS style-able. Bitmap icons feel a bit 2008.

This would make sense if they were vector icons but because it's a TIFF you can't really do any resizing or worthwhile editing.