There is a bit of a different blade feel to a larger razor, which some people love. Personally I stick between 4/8-6/8 and rarely stray from this.
As far as why larger blades? Well back in the day, most men didn’t shave themselves and visited the barber weekly or even daily. There were many razors marketed to barbers called “for barbers use” or “barbers only” razors. These razors were mostly all 7/8-9/8 and were made large, so the blade could hold more lather on in per pass. This is so the barber would not need to stop and rinse or wipe the blade off quite as often as a smaller razor would require. Thus, the barber could finish his shaves faster and move on to the next gentleman. These blades also would have lasted a bit longer and could have handled a bit more honing and wear than a smaller blade.
Now, many larger razors such as the Wade and Butcher For Barber Use and the Filarmonica 14 were made originally as barber razors first, thus their hefty size. Naturally, the average joe did not typically need a huge blade for his morning routine and didn’t not need to pay for all that extra metal. Now days, it’s in fashion to own big blades! Do they shave any better? Maybe, it depends on the person to be honest. The one thing you can be sure of is that a larger blade will cost considerably more than a 4/8-5/8.
So it’s all up to what a guy likes. I recommend everyone try a big blade at one point, but definitely the starter range of 5/8-6/8 is perferred especially due to cost and maneuverability. Believe it or not, a 3/8 & 4/8 can provide an amazing shave and they are very inexpensive to buy and they are even more maneuverable than a 5/8.