Food makes you retain fat. :P Just kidding. In all seriousness though, no food makes you "retain fat". You gain weight when you eat more than you burn.
I don't know about other people but I use whey protein because it has a lot of protein per calorie. It helps me recover more quickly after a workout and it's convenient.
There is no harm, but there is little evidence of any benefit.
So eating more protein with controlled calories doesn't have benefits?
Oh man, if I had come across that image before I would use it at least once a day in these forums.
Its good but not necessary if you can get protein out of whole foods. It has a huge convenience factor since its quick and easy, so if it fits your lifestyle, enjoy! Whey has better absorbtion and bioavailabilty than eggs. The only pit fall would be excessive use over long period combined with a lack of fiber can contribute to intestinal problems and has been linked to celiac disease. So its not a meal, its a supplement.
The side effects of allergy medications keep some people from using them. Natural remedies can be a great alternative, but some are more effective than others.