What are some reasons to genetically modify plant metabolism?

well commercially everyone would stop buying them as most people fear the side effect as we do not enough about gm crops or plants yet since it is fairly new. What if this plant then somehow bred with another undesired plant like weed?

The main positive would be the increased speed of growth of the plant. It would fruit quicker. Probably be bigger itself. Metabolism is basically how fast or how much energy you use. The faster/more energy the plant consumes, the faster it will grow. Flavours of fruit may not dvelop enough though as the flavours would probably not be sped up by the increased metabolism.

There are several different types of fruits with plants.  We automatically think of oranges, apples, etc.  But "fruit" is a very general and misunderstood term.  The Bean family, like peanuts, peas and the like have a fruit that is labeled and called a pod.
They are not fleshy fruits and are also not to be considered by most people, fruits at all.  To genetically modify plants at all, would mean to change the fruit/flower reproduction as well.  It could very well be possible to make fruits of certain plants much larger and more fleshy, the fleshy part is what we usually eat.  The larger the fruit, would also entail that the plant would be exponentially larger as well.