When I was a kid, we had chores to do around home. One thing I noticed even back then was that everyone has different work styles and habits. I preferred to plow through the work, get it done, and then have the rest of the day to do what I wanted. That carried through to my adult work life as well. My younger sister, on the other hand, had a different work style. She would start on her chores, get them partially done, and take a break. She'd return later to do more chores, then take another break. Being a stay-at-home mom for 3 young boys now, I doubt she gets the chance to take so many breaks now!
I notice something similar when working with dogs. Some will work, work, work and aren't concerned about taking breaks. Other dogs seem to prefer the frequent-break work style. If you know your dog well enough, this can help with your training. If you are one who likes to keep working but your dog isn't, you might actually be more productive in your training if you take frequent breaks. Sometimes we try to push our dogs for too long without giving them a break. On the other hand, if your dog likes to work and you like to take frequent breaks, your dog might start to lose interest. Hopefully, you and your dog have similar styles, but if not, consider finding a compromise that works best for both of you so neither one of you gets frustrated or bored.
Taking breaks can be a good way to re-energize and be more productive. I'd rather get three great five minute training sessions in with short breaks in between than a thirty minute training session of mediocre work when I spend more time trying to keep my dog focused.
Give your dog a break!