I'm a new homebrewer and have a newbie question: can I skip the mash out time just replacing it by sparging since the water temperature is the same? What kind of things can happen doing this?
Like many all-grain brewers, I used a cooler for a mash tun making it difficult to raise the temperature to mash out. I still made good beers.
This step achieves two things.
First, it halts enzyme activity. If you are really, really good at mashing you know exactly when you have the perfect mix of fermentables & unfermentables in your sweet wort and any more exposure to enzymes would change the beer's profile.
Also, the heat makes the sweet wort and grainbed less viscous. This makes it easier to lauter & sparge because the liquid flows more freely.
If you are brewing a beer with a large percentage of wheat or other gummy stuff a mashout may help. In most cases you can skip right to sparge.
Mashout is useful at the homebrew level if your wort is going to be sitting in the kettle for a long time prior to boiling and you want to lock in the mash profile. The other thing Mashout can help with is boosting poor efficiency a little bit as the warmer temp improves the viscosity of the wort a bit.
Aside from those two areas, I don't routinely mashout either.
Remember that to denature enzymes, you need to hold that 170+ temp for 20 min. or more. Few homwebrewers do that. While it was once thought that hotter sparge water reduced the viscosity of the wort leading to easier runoff and increased efficiency, that has been pretty well disproven by the work of Kai Troester (www.braukaiser.com). What does happen (and does increase efficiency) is that the higher temp leads to a more complete mash conversion.