I was taught that sharpening by hand takes no longer than an electric one and produces better results. I leave the chain on and mark a tooth with a sharpie. Sharpen all then left then the right. About every fifth sharpening I'll hit the rakers, a very important step that I find few know.
Was told an electric grinder Sharpener does more damage to the chain than hand filing therefore shortening it's life span.
I also find it takes no longer to hand file a chain on site than if you were to change chains. So no need for a tangled web of sharp and dull chains to sift thru.