The irony is, the heavy effect only occurs when you're riding a mount - and there in lies it's true purpose. In 1.0 this effect was actually called 'lamed', and only affected your mount not you (hence it made your mount run very slowly, and disappeared when you dismounted). Because enemies are leashed and will de-agro once you get far enough away from their 'patrol area', the 'lamed' effect on a mount was to compensate and to give this sense of danger.

So I was a bit disappointed to see it named 'heavy' in ARR and actually affect the player and not the mount (it stays with you if you dismount). Still, I don't see this masochistic obsession some people seem to have with wanting zones to be deathtraps with a million ways to kill the player, as it just would ensure no one would even bother doing content (plus would make things unfair to low level players).