One thing to keep in mind is the time of year you're traveling. If you go during a time when the parks are open late (summer, spring break, late December), then an afternoon break might make sense. Especially in the weather is really hot and humid! Afternoons are the hottest part of the day in the summer, and getting away from the heat, humidity, and crowds is smart. Go to the parks early, take a break after lunch, then go back late afternoon till the parks close.
If you go during a slower time, when the parks close fairly early in the evening, afternoon breaks might not make sense for you. I usually go in either October or February. Park hours are shorter, with AK closing at 5:00 pm, and the other parks usually closing between 7:00 and 9:00 pm (except for those with an evening EMH). If you take a long break in the afternoon, it really eats into your available park time.
Here's my "math." Say a park is only open from 9:00 am to 7:00 pm. That's 10 available hours of park time if you stay from open to close. If you take a break, it can take 30 to 45 minutes just to get back to your resort if you're taking Disney transportation (or potentially longer if you're staying at a non-WDW hotel). Count on another 30 to 45 minutes to get back to the park, and you're talking about a potential of an hour and a half just for travel time. Add in a break for an hour or two, and you'd be taking about ~3.5 hours for your break. If you only have 10 hours of available park time, you've eaten up about a third of your potential park time for a break. Not so great, right?
So when I see the advice of "take an afternoon break" here on the DIS, I would say that you should take that advice with a grain of salt. Even if you have little kids that are at an age where they nap, I have heard some folks say they try to get them to "stroller nap" or maybe take a break in a nice, air-conditioned restaurant as an alternative to going back to their resort.