Now, the world in Hostile Sector is not exactly round either, but at least it contains height features. And more importantly, it's not merely a cosmetic feature, but provides important gameplay as well, some features more obvious, and others less.
These are the two basic features that you get "for free" with height differences. The following are less obvious, but provide additional depth for a turn based strategy game like Hostile Sector.
The disadvantage is that slopes are cumbersome to move in.
So, as you can see, height creates interesting tactical opportunities, and is by default a good and balanced gameplay feature. The advantage of being positioned there, is balanced by the difficulty in getting there (and sometimes getting out of there).