First of all, define *useful*.

It depends on you, if you want to *catch'em all* or if you want the strongest one. Or maybe you want to evolve Pokemon. 

 - Evolve: eggs are useful. It gives you a good amount of candy. See: http://gaming.stackexchange.com/questions/276005/how-many-candies-do-you-get-for-every-2k-5k-and-10k-egg

 - Strongest: it depends on when did you get the egg, not when hatched. 

 - Catch'em all: You can get 73 pokemon by egg