Step one of brewing is to drink brew while I brew! But I write everything down in my log to refer to later - measurements, observations, things that go well and things to improve on.
It's great to check that one beer I had hiding in the closet that aged amazingly well. Now I have a hope of repeating it.
Yes, but I typically don't start drinking right away. I usually brew 2 beers back to back so brew day runs from about 8 till 3. I'm usually multi-tasking with making breakfast or doing things around the house while mashing and getting the first beer to a boil. Then I'll start drinking around 11 or 12 when the first beer is going into the carboy.