The rakers are commonly missed by many who sharpen a chainsaw chain.
We used to take the rakers down a bit on a new chain a bit right out of the box. This was when I was running a professional saw with lots of HP. There is an increased kick- back risk when doing this and I wouldn't recommend it for the occasional user.
The factory sharpen on a chain is done so that the tooth has an almost honed finish. This is hard to do unless you have a real good sharpener and a well dressed stone.
I usually use a file to sharpen my chains unless I have hit a nail or stone and the point of the tooth is knocked off.
The second common mistake is to leave a burr on the cutting edge of the tooth. This will break off when you first start cutting and immediately dull the tooth somewhat. So when I want a sharp chain I file into the cutting edge so that the burr is off the back of the tooth rather than the front.
I knew a chainsaw competition pro who sharpened with a file and he was meticulous about not leaving any burrs and always filing into the tooth. It's not an easy method to learn because you have to roll the file at the end of each stroke to pull the burr down and file it off.
I have toyed with the idea of grinding a chain and then honing it to see how sharp I could get it...........but I don't know if I want to spend the time to do this so it stays in the 'ole brain box....rattling around.
I once was asked to help clean up a 9 acre woods by a friend. He had 2 descent saws so he told me to leave mine at home. They were Stihl 042's and I figured they would work well. They were so dull that I brought files with me the second day and proceeded to sharpen the chain on the old saw I was using. After a few minuets of me cutting fast and efficiently he came over and said that his new saw wasn't running right and wanted to trade. Well, I went ahead and sharpened the new saw up and soon he was back and wanted to know how I had gotten his new saw to cut so well.
I gave him some sharpening lessons right on the spot.