Well, past the "best course for the fish" pros and cons, let's explore this a little. For purely visual effect, anyone would say don't do so. I've seen some giant gourami's come into the lfs that have magic marker designs on their sides and even something so common should be left out of the hobby. It's only a few steps away from tattooing your animal, or even better using the free space for advertising.
Now if aros are anything like betta's, the showers will nip and trim to provide for that excellent look. No big deal as long as the fins are not nipped too low. If they are trimmed too close to the body, they won't grow back right. In our's he's getting older and his fins have never stopped growing. Not nearly his original majestic beauty, but I can't imagine trying to sit him down long enough by any means to trim the fins. All in all, we really have to ask why we have the fish. For personal preference, I tend to go with nature. Trust me it is a fine line to try and walk. Unless the fin poses an obstacle to the day to day survivability of the fish, leave it be.
Just my two cents. Swim on!