if you use platform all around you can use wall height 2 or 3 and still make it look wall height 1 this makes it so you can use roof trims that for some very annoying reason are only available to wall height 2 upwards
also with platforms you can make huge "staircases" which you can't if you add foundations
as for cons you can't make pools through platforms and you get limited selection on wallpapers because plaform goes over them
also might struggle with wallpapers for exterior with the platform look
as for pros of foundation well you don't have the wallpaper struggle you can build pools through them and its also much simpler to build cause you don't have to fiddle with platforms and whatnot
oh and i don't think we can place ladders through platforms but i might be mistaken
aand if you did want tall walls and foundation the platform would make wall height appear shorter