I used to sharpen chains professionally, and now run a firewood business. Files are safe in the forest because they don't spark, but I prefer other methods..... I start the day always with my chains sharpened in a proper drop-down disc type chainsaw sharpener, and after that, sharpen them in the field because it's quicker. Don't forget to hand oil the chain on remounting it, and grease the front sprocket daily if its greasable).
Every few days I correct the raker tooth height, you CAN do the raker in the electric sharpener by changing over to a wider disc, but I prefer to use a file and a depth gauge for this part, I'd almost have the job done by the time I changed over the disc. I use an old bar held in the vice to hold the chain. It's quite quick, file the raker tooth from the "off side" so the file cuts nicer(ie do ever second raker, then turn the chain around and do every other raker. In softer woods (I do a lot of willow) I use a depth guide at 30 thou instead of 25 thou and get nice big chips, I still have the power because willow is easier to cut. Always use a gauge for the rakers, more (taken off)is not always better, because it will slow the saw down = no power and hard on saw
In the field I sharpen the chain very quickly with a hand held 12 volt sharpener(like a dremmel tool). Mines a stihl, and I've found the white emeries from Stihl are good(last a long time and don't get hot quickly). The field sharpen is just as sharp, but the reason I use the other as well is that a drop down disc grinder is more precise, both teeth are the same length, and this goes a long way to avoiding curving cuts and/or lower performance from a mix of short and long teeth.
Other comments are that if you are cutting large logs, say over 24", try a skip tooth chain. Twice as quick to sharpen, and seem to stay sharp the same amount of time. Nice to use as they require less bar down pressure. On small logs they're usually slightly slower, on larger logs often faster, they don't drag the revs back so much. As you will probably know, 2 strokes power is all in the last few hundred revs at the top end, you will kill you chainsaw by labouring it (overheating),keep it revving! I literally get thousands of hours out of each chainsaw (I use Johnsereds, but the comment is relevant to all 2 stroke engines, especially air cooled). If you can't obtain a cross-cut skip tooth chain, more common is a skip tooth ripping chain. They are fine for cross-cutting, just sharpen the 10 degree rip angle to 25 degrees before using.
If you don't do a lot of sawing, the cheap disc sharpeners are good value. Tip....Mount them on a piece of wood using 4 rubber door stops as feet, instead of bolting it to your bench. This makes it portable, and it will sit still. Add a piece of metal to the rear for a counterweight, and cut away the timber at the front so the chain hangs nicely over the front of the bench, and you'll be sharpening like a pro.
Hope that helps.
