No point nowadays, but one of my early bikes had a double with 3 teeth difference. Something like a 52/49.
On the rear was a 5 speed block in 2 tooth jumps. 14,16,18,20,22
The idea being that you could go/up down at the rear and on the big ring and when you felt that you needed something in between, just move to the smaller of the chain rings. The three tooth difference gave a ratio mid way between the sprockets.