I like the idea of a disc-world, but I've never been able to come up with a satisfactory way of explaining how a day and night cycle would work.
I found this gif somewhere on the internet that does the job. Though it would have been better if I'd had the concept in mind before I started drawing the maps, because now I'll have to rearrange everything to cater to having the icy frigid regions in the centre and edge rather than top and bottom. It's not a huge deal, fortunately; it just means that north and south become in and out.
So, why bother? Well, why not?
10-hex hex grid I designed a few days ago, with 1000 mile hexes on this map.
I've had to move and rotate the archipelago to get its arctic areas to align with the centre and edge frigid zones, but apart from that it doesn't really affect anything that's happened in any of the campaign to date.
In fact, the whole flat-world thing has very little mechanical impact on anything. It's pretty much just for flavour.