The plants can help clean the air for us. ( I personally want one of each of those indoor plants! :-) )
The trees absorb carbon dioxide for us, unfortunately the cut-down of rainforest is not helping the climate change. In turn the climate change is not helping the trees and so we have created a bad spiral.
There migh be unexpected ways plants can help us, they can for example work as a natural guard.
A lot more plants than the avarage vegetables are also edible (link in Swedish) and I think we often forget that a lot of herbs and plants can be used for the most ailments we have.