Why skip the mashout? I've only recently been able to step mash, and only slowly so I don't do a mashout step, but just curious how this could cause issues?
The primary issue, aside from just the general increase in complexity with an additional step — more steps equals more chances for mistakes— is increased extraction of things you don’t want, most often tannins.
But more to the point, what’s the benefit? It potentially could make sense at larger scales, where the decrease in viscosity at higher temperatures could speed up sparging. The arguments about “locking in the sugar/carb profile,” I.e. “stopping enzymatic activity” also don’t make a lot of sense. The enzymes denature in the boil anyway, and what’s the difference if alpha amylase gets an extra half hour on your wort?
In my opinion, it’s one of those things that professional brewers do, that maybe make sense when you’re double- or triple-batching 10s of barrels every day … and then homebrewers decide they have to copy. I think it’s hard to argue it does anything meaningful for you when you’re making 10 gallons in your backyard. And if you’re doing 5 gallons with BIAB, it pretty much can only make things worse for you.
It’s my opinion, and not necessarily widely held. Folks can (probably will) chime in to say what I’m missing.
Funny you mention it, I've recently switched to liquid yeast starters. I've definitely wondered if this could be part of my issue, as prior to this I was over-pitching dry yeast and was better success on what I would view as poorer executed worts.
With dry yeast, you need to worry much less about the age of the packet, you get to forget about oxygenation/aeration, and (given package sizes and expense) it’s much easier to pitch enough cells. Liquid yeast certainly has its fans (can’t match the range of choices!) but if you’re trying to remove possible points of failure as part of troubleshooting, I think dry yeast is the clear way to go.
I don’t believe overpitching is ever really a concern for homebrewing. Underpitching can give you a bad beer. Overpitching will not. It may be a
slightly different good beer than with a correct pitch, so yes, if you’re shooting for professional-level batch-to-batch consistency, make sure your pitch stays the same.