A good question. You can actually do either and the potato will produce a potato plant and a crop of potatoes. The real purpose of chitting potatoes is to make them produce a crop as quickly as possible. The little sprouts that appear when potatoes are chitted should be around 1 to 1.5cm long when planted. If they are shorter they will not produce the earliest crop. If they are much longer the sprouts will probably get knocked off when you plant the potato seed. I would think that 4 or 5 inches is too long unless you take a lot of care when planting the potatoes. I cerainly have never trimmed them, I would just rub thenm off and wait for more to appear.
The link below goes to a page that describes all this in more detail. And if you click on the third picture down you will get a large picture of a chitted potato that is about the ideal size for planting.