First of all, you already know them. They are the magic behind the taste and texture of the McDonald's cheeseburger.
Lately I've been experimenting with their substitution for fresh-diced in various dishes, and it's enjoyable.
Some advantages seem to be:
-the sulphenic acid problem of eye burn when chopping fresh onions
-the weight of dragging fresh ones on the subway
-the long storage time vs fresh
-the taste becomes richer and more concentrated, just as in dried mushrooms
-the chewy texture that remains after reconstitution with water
-the price of fresh onions at the grocery just won't come down. Gone are the days where loss leaders ads priced them at 19 cents a pound
So... where do you use them? Where have you wanted to use them? Does the purist within you impede you from enjoying them?
For example, I've used them in several bean dishes in place of fresh. Also for "French onion dip" knockoff by barely reconstituting with soy sauce and worchestershire and adding to sour cream.
(Links to previous threads appreciated)