If you are running DMX 500+ feet, I would highly recommend a DMX Branch or Opti Splitter of some sort. More then 1000' and you will need one because the signal drops off at that point.
An opti-splitter does more then isolate. It also helps amplify DMX signal like a DA (distro amp) does for video. The isolation also isn't for lighting strikes, it helps if you have faulty power or your console and fixtures are running off of a different ground. This can cause problems just like in audio, though not as pronounced.
Also, if you are using more then 6 types, meaning dimmers, moving lights, LED fixtures, etc, you should use a split, running each source into a different section of the split. You will start to have issues and things miss communicate. Dimmers aren't really a problem, LEDs are a huge offender though. 8 max LED fixtures per line. Movers are generally 16-32 per line. Terminating also won't fix this.
These reasons are why you will see large shows have racks of splitters, with another next to the console as well. It helps eliminate problems. Generally they will do a data line per truss, or section of truss, or electric. Just one more thing besides terminating that can help with issues with data.