My opinion only.
1. Yes, for TRUE beginners. I'm talking like the first couple of times they're picking up a fly rod, just trying to get a fly out far enough.
Generally because true beginners aren't casting very far, often not near the amount of line the rod is rated for. Hence, a heavier line will load the rod more properly, as well as allow the caster to feel the weight and understand the timing.
2. In short order, though, I think it reverts to properly weighting the rod. That said, again, it depends on what type of fishing they do. I think the standard for properly weighting is 30 ft of fly line beyond the tip, meaning with leader and rod length, that's fishing 40+ ft away!
Personally, in PA for sure, and perhaps most places for trout, I think that's an unusually long distance even for experts. i.e. by matching the rod rating with the line rating, most of us are actually underweighting the rod, more severely the shorter the distance. And the trend of under-rating heavier rods just compounds the effect.
This is all because when we test a rod we like to bomb casts out there, and the one that bombs a cast the best, we like the most. It's just stupid because we don't actually fish at that distance. But they sell what we buy. So if they label a 6 wt a 5wt, we put a 5 wt line on it and compare it against actual 5 wts. And guess what, it feels the best at long distance! We like it and buy it. Then the competitors catch on and do the same....
By now, our 5 wts are what old timers called 8 wts, lol. And if we stick a 5 wt line on there we can cast the whole dang line and congratulate ourselves on how good we are. Nevermind that we can't cast accurately at 15 ft, where most of the fishing is done!
So, to summarize. After only a few outings when they get the basics down, I think beginners, like the rest of us, would do best with a properly loaded rod. But marketing is such that most of us, even veterans, are underlining and could use to overline a little.