I think it is the greatest thing to have live plants in the aquarium. However it also depends on what type of fish you have. I have all real plants in one tank with my sweet little community fish they seem to like it. I need to add better lights for the sun loving varieties of plants. My other tank which is full of cichlids has no chance for real plants. Sure I could get plants that float or they better because the cichlids are always moving rocks and uprooting my fake plants. I find it kinda humerous, you never know what the tank will look like from week to week. Snails like to eat some varieties of plants I have heard. I am planning on adding more plants for my Angelfish to swim around in. I will probably turn this tank into an all real plant tank also.
Plants are beneficial in adding oxygen, etc. But if they don't get enough light or nutrients they may die and pollute the water. Rooted plants also make it harder to vaccum the gravel if you do. The Java Fern is a plant I have found to be virtually indestructable. Well that is some of my 2 cents. Hope some of this might give you some insight.