I felt like there was pressure on me to try and carefully balance out how many of each thing I had (assuming that's what it meant by balance) and I tried to make it about equal, instead of actually enjoying myself making something that looks nice like I would do in RollerCoaster Tycoon.
I just checked the manual and it also doesn't explain what it's measuring.
I guess I can just try to make a pretty looking park later in free play mode, now that everything is unlocked from playing levels.
@NovaSquirrel I remember playing legoland a bit, but I was a lot more interested in lego creator