So let me ask....
Are you training 7-days a week, thinking that you need to hit-it every day in order to improve?
Do you feel you get enough rest in between training sessions, or that a complete day of rest is only for novices?
Does training every day make you feel "tough"?
If any of the above describes you, beware. Worst case, you may be slowly drilling yourself into a hole that you'll have a difficult time getting out of. Best case, you're probably not recovering enough to be able to put the maximum amount of effort into your most important training sessions, which are ultimately what lifts your fitness to a higher level.
In my book, 1 full rest day each and every week is absolutely mandatory, regardless of your level of experience or what races you may be training for. The mental and physical break can help make your other training days more productive and ultimately help you lift fitness and boost recovery beyond a level it might have other wise been at. And it might help you stay free from injury too!
Remember, your next training session is only as good as your last recovery.