You need rest in your triathlon training to be successful and to achieve all of your goals. Even professional triathletes need rest in their training. I have even heard of triathletes attempting to maintain 10-12 hours of sleep per night. For most of us, this is not feasible with our family, work, and training schedules. I know that rest seems counter intuitive for better results. It seems that you should push your body to it limits everyday and see your gains come through this type of training. The issue is that you will burn out before you see your ultimate potential.
REST AT NIGHT
One of the critical areas of rest is to get enough sleep at night. Triathletes need 8-10 hours of sleep per night. I know, I know that seems impossible. In fact with 4:00 am wake up calls there never seems to be enough time to sleep. I suggest trying to get to bed as early as possible avoiding some of those things that keep you up like TV, Facebook, Netflix, video games, and others. This will help your training from day to day. If you do not sleep enough you will increase your chances for injury and burnout.
REST DURING TRAINING
Triathletes want to train and they want to get better. They strive for more and more training to increase speed and strength. However, sometimes you hit the wall. Many triathletes are type A individuals who live off of a checklist. So, if there is a workout scheduled for a certain day they will get it done no matter what. So whenever you hit the wall you may have to take day off. I have found this to be incredibly difficult to do unless I am throwing up. However, I know that sometimes I just have to take a day of rest.
REST THROUGH PERIODIZATION
You cannot train for months on end without a break without experiencing some amazing difficulties such as injury and burnout. So, you need to determine when a race is approaching and count back from that date and set up a 10-12 week training plan. The other time needs to be spent in lower heart rate training developing your aerobic base, working on form and skills, and RESTING! You need to rest some in your training outside of preparing for a race. This will help your mental as well as physical state.
If you want to see the big gains in triathlon and get to the top, make sure to rest well.