Are there any potential repercussions to building on an island set below the normal "0" level, or building a town with a shoreline water level of plus Minus 2000?

After resizing landmasses I come across this issue where I've actually built something several hundred props in size and rather than toy about with levels............... I ask do I need to worry?
Thoughts make me wonder about shadow detail? Wierd render cutoffs? Anything like that?