Many of the world's great beers are made with one malt and one hop. Much depends on the style. Obviously the one malt will be self-converting, which rules out dark beers. The description SMASH has become fashionable largely for APAs, AIPAs and NEIPAs that normally use two or more hops. Still, one can get a lot of complexity and smooth bittering out of Mosaic alone.
Sometimes you want to feature one hop's distinctive character. Stone and Wood's Pacific ale, using Galaxy alone for flavour and aroma, is an apposite example. Galaxy gives a blast of what the breeder calls passion fruit, but many hops say that. I'd go with peach. Whatever, It works. I believe there has been some discussion here whether they add another hop for bnittering.
Two beers tonight, Ordinary Bitter, one out of the bottle the other out of the King Keg. Both the same beer but mouthfeel entirely different. The King Keg is far smoother most likely to the lack of carbonation.