To stretch your heli is just a matter of personal preference in my opinion. Some choose to go with the longer tail boom and longer main blades because of the fact that longer blades increase the lifting capacity of the helicopter. However, quite a few people manage to get the job done with a stock setup. If it’s something you think you need to do with your own setup, you can find more information in the Helifreak forums under the aerial photography section. You will of course however, need to sign up for that site.
Here is a stretched Trex 600 model