Sure if someone asked me why I would take them or why they were good I would tell them because they help aid in recovery, to prevent the breaking down of muscle tissue, and in the case of Optimum Nutrition's Amino Energy, for an extra boost due to the caffeine in it. Like I said though I didn't really think much of them other then as a tasty way to flavor my water with possible benefits to help recovery and they are cheap, win win... Well it has been about 6 weeks since I've taken any amino supplements, but it hasn't been until recently that I noticed ever since I stopped taking them that not only has my workout intensity dropped somewhat, but more importantly that I'm getting sore after workouts now. Especially when I train legs heavy, I'll be sore for 3-4 days after.

Now for those of you interested more about amino acids and their functions I found a great article by Ben Green, which goes on to explain exactly what they do without being boring and making you want to fall asleep while you're reading... Definitely take a look!
http://www.bengreenfieldfitness.com/2011/04/do-amino-acids-really-help-you-exercise-or-are-nutrition-supplement-companies-pulling-a-fast-one-on-you-part-1/