It just clones half the map. If you have stuff going to 72, then I bet the stuff from 64 to 72 would be replaced by the tile stuff from 64 to 56. I haven't used it =/
well, i used it in my recent maps
a good tool, very aiding
you can concentrate much more on balance/concept/layout than to count how many tiles you have to go left or whatever
lmao thats what I do count for long time making sure everything is exact. Sometimes i get super far then when something is coming together they are off by 1 tile & i'm like DOHH!!!!! & have to redo the whole thing :D
i am currently constructing my 3rd map and for the first time, i'm trying out the symmetry tool. i can tell you though that like what nightmarjoo said, it isn't completely perfect because of how close the low ground is to the cliff. you can have like jungle touching the bottom of the cliff at some angles and others you won't be able to do that without manually fixing up the terrain.
The symmetry tool is more useful for the general layout, high dirt/dirt etc. For deco I wouldn't insist on symmetry anyways.
There also is the difference that the front cliff from stuff like high dirt to dirt is 3 tiles high, while the backside is only 2 tiles. Keep that in mind.