Thanks,
The more detail and res the images are the further you can zoom in to them. The usual way to create the world is to start at the top and do continents and detail them right in. Then go down and do it all again and so on until you hit cities and then make a fully detailed city map. The thing is that if you start with houses or the city then when you do the region the app can fill in the city for you. then as the region gets detailed the continent starts getting done for you etc. So whilst its true that its good to have detail, it might not be the best strategy to put the effort into to making every map wildly detailed. Better to put the effort in at battle scale and let the app do the work for you. Also, all the upper scales get modified automatically when you change the lower detail.
Its like a sculpture. You start with a blank block. You wouldn't chip off the top corner and detail all that in right away. You rough it out and then progressively work on it.
Another thing thats worth bearing in mind also is that you can reuse branches in the mapping tree. So if you make a fantastically detailed inn for one city, you can clone that and use it again - or even bits of it again. It takes no more storage to do it. The app gives you either option of having each of them unique or you can use exactly the same icon so that if you change one then the other gets modified also. So you might want to change the name label and the characters within but tie up the basic layout. Thats handy for generic villages or basic houses when somebody creates a new icon - like those Persian rugs for example recently. One quick mod and every generic house in the world gets a new rug. Of course you do have to be a bit careful when editing a global generic / template icon.