There are a bunch of those small tips when it comes to cooking. Many are true, many aren't.
Another one here was breaking apart the mushrooms vs cutting them. That made me think of the difference between garlic being pressed/minced or chopped. Depends on what you want out of it.
Right- so another food pedant point-
So much of cooking knowledge is based on "tradition"- and much of it is demonstrably silly and wrong as AnotherDuck noted, but was passed on because that is how a person did things without repeated experimentation of variables, and because they didn't want to get things wrong. So, many things that had nothing to do with the result were recorded down as essential- you will find recipes for whipping egg whites to ONLY whip in one direction, something that has nothing to do with how meringues form.
The "don't wash mushroom" issue has been debunked multiple times- though it has caveats, and like anything, depends on the preparation and type of mushroom. Most important to note- mushrooms grow in detritus- or worse/trash/molding logs, etc. It's actually SMART and SAFE to wash them. YES- mushrooms will absorb moisture if washed, but VERY minimal, and if they are being cooked, this matters little since the moisture will either evaporate if searing/sauteeing, or will be added to soups/stocks if wet cooking. This is a good primer on the topic, specific to things like shiitakes as this manga chapter alludes to-
https://www.seriouseats.com/knife-s...mushrooms#toc-how-to-clean-shiitake-mushrooms
Wash just before using, since moisture will accelerate bacterial growth and spoilage. The important thing here is after washing, remember to dry them, either in a salad spinner or with paper towels and air dry, as this allows for better browning/maillard reactions when searing/sauteeing them since there is less water to interfere.
As for washing things like truffles, which are often stored in dry rice to absorb moisture (again, another kinda silly tradition, since dessicant/silica/calcium chloride packs would do much the same, without the risk of surfaces for bacterial growth), it's kind of a similar point, but different order. They grow in dirt, or worse- wiping with a damp cloth is the standard. Whether washing them fully and then spinning/patting/letting them dry and storing away (in the manner above in rice or more modern methods) is better, I'd leave it up to the person using them. Most restaurant truffles are received pre-cleaned in the damp cloth method, or only dry cloth (hence doing it yourself before usage) and stored as listed above, so unless you are lucky enough to forage yourself, it's not really an issue. The point here is that you would be eating these often raw, shaved on top of dishes to finish, etc, and so would not want added moisture from washing.