If you PvP, being able to cast while running is great.
If your not PvP, then in certain bosses in later instances, where you need to be moving around, you can re-apply it during those times and keep your DPS up, while you wouldn't be able to if you had to stop to cast.
Just about any way you look at it though, it's a better choice than suppression. I mean a couple points in Supression can help, but 5 is way over the top.