There was a time when it actually made sense. When there were few grades, big visual differences between grades and price differences between grades that didn't make the greater fool theory into an institution.
My opinion, where slabs pay off is that tricky VF-XF indecision, especially on coins you don't see very often, like half cents or 20 cent pieces, etc. And I'd rather have near-completion in MS-60s than a bunch of holes with a couple MS-64s and little else.
As a collector of 'modern' commemoratives I find no real need to to get or have them slabbed. I enjoy them in their OGP holders. I've always contended that the grade game with these has been to make artificial rarities out of otherwise common (high mintage) coins.
I seriously recommend you get into collecting European coins if you're nostalgic for that. For the stuff I collect, nice mint state is twice the price of nice extremely fine, which is probably where it should be, and less than 1% of coins are slabbed.
Just a few years ago I was buying military tokens by mail bids from a dealer whose grading system was =average -below average + above average.
Condition isn't everything, it's the slab that matters. Would it be wrong to call the ultra fine granularity of the Sheldon scale to be the underlying problem, and the idea of visual appreaciation to be represented by linear scaling?
Sure was... and I certainly enjoyed collecting back then (1950's). I still enjoy it though, as there are plenty of coins free from "plastic entombment".