What is the purpose of genetically engineering crops?

its cheaper to make and can be make all year long without worrying about the season. if u get a chamce watch food inc and u'll see alot of those GMO's

Increase quantity or quality of harvest.

there are several reasons to genetically engineer crops, here are a few:

1. Disease resistance: peaches and other crops are highly susceptible to fungus, genetic engineering makes them immune to some strains of fungus
2. pest control: some crops are genetically modified to produce toxins that kill or make a crop taste bad to a pest such as aphids or locusts UC riverside has made oranges that kill wasps
3. Hardiness: crops have been engineered to resist cold temperatures or grow in soil with too much salt for normal plants
4. nutrition: rice has been genetically modified to produce vitamin A, as rice is free of many essential nutrients, yet is the main food source for many people in the world.
5. drought resistance: crops have beeen genetically engineered to require less water and survive dry seasons that would otherwise leave a population starving to death if rain does not come once every two weeks.
6. Taste better: one lab has genetically engineered broccoli to be less bitter so kids will eat their vegetables!  
7. food production: crops have been genetically engineered to produce more pounds of food per plant for a more efficient harvest.

there are more reasons, like less dependent on fertilizer, and others but the possibilities are endless!

There are some down sides = disadvantages which sometimes don't appear until long after the GM = genetically modified food is on the market
1 people with food allergies may be badly effected by a GM food, but not by essentially the same natural food. In the USA, it is illegal to label food as Not GM. Monsanto, boo-hiss.
2 The GM plants may go wild and derive useful natural plants of habitat.  Neil