GRS really pushes this type of heel... but I don't think Sam mentions it in his video, does he? I guess it makes sense if you were making really wide cuts... but other than that, is it less forgiving for a beginner?
I use a standard 90 or 120 degree graver (120 mostly), and the majority of my graver heels are about 1/4mm long. Shorter heels help to minimize heel drag.
Long heels were what I learned when I started engraving jewelery. But in those days the square gravers, which I think were just tool steel or some high speed tool steel used to break pretty often. Consequently we used to keep the heels pretty long since it was faster to sharpen just the top face than to constantly have to work on the heel faces.
But with the advent of the GRS sharpening system the only reason to use a long heel is just not knowing any differently. When I took the course with Sam Alfano he emphasized the short heel length. So short that it looks like a sliver of brightness at the end of the tool. But after trying it for awhile that's all I use and teach.
I'm now using Steve Lindsay's graver geometry but keeping the heel at .025 -.05 mm in length. Works real well for me.
When I started many years ago we were taught using long heals, but we were using oil stones to sharpen and it was easier to sharpen with a long heal and as Allan says, you only had the face to sharpen once the heel was sorted. Only time I use them now is on long straight cuts. I use the uniform heal for really deep cutting, motorcycle engine covers, I haven't found them anymore difficult to use. Mind you I'm really behind the times...... only just started to use 120's in the last month or so.