Well, the only reason scientists try to do anything of this sort is to somehow make the organism better in some respect than it occurs naturally. Take corn, for example. The corn we eat now, the ears of corn we recognize in the produce sections of grocery stores, is a far cry from the ancestor it came from in old Mexico. Those ears of corn wer half the size of what we have now, and the kernels fell off the ears before they could be gathered and eaten.
Then there's the case of the "super-salmon" also referred to as the "frankenfish". Scientists were able to introduce a genetic code into a regular salmon that allowed the salmon to produce growth hormone the year round, so the genetically modified salmon grew at a rate of three to four times as large as the regular salmon.
Is it safe to eat? It depends on who you ask. Everything in the produce section at the grocery store is the result of man "tinkering" with selective breeding, naturally isolating the characteristics of what he wants in those vegetables and fruits. The proponents of the supersalmon say there is nothing wrong with the fish interms of eating them, no negative health risks, and they taste just like their naturally-occurring counterparts. There are still those, though, who feel "you just can't fool with Mother Nature" too much and not pay a price somewhere along the line.