I've only been tatting for a few years now, but I'm been knitting and crocheting for decades, so I should really know better by now.
If you're new to your craft, you're probably still dutifully following patterns with very little modifications, but after a while, that will all change. You will find yourself working along and think, maybe I should change this or remove that, so you do. Then when you look at the final piece and think, wow I should write those changes down so I won't forget them. Listen to yourself!!!
I really have lost count of the times I've designed a pattern on the fly and didn't write it down only to find myself counting the teeny tiny knots in the finished piece weeks later. Even worse, selling the only piece and trying to reconstruct it from the pictures I took for the listing. I do have a little notebook, right next to me in my little crafting corner, but I seldom reach for it. I did recently start making prototype pieces in easy to see white thread, but that still leaves me counting knots over and over again.
I can't be the only one with this problem, right? There are dozens of you out there nodding along in agreement, I can hear the rattling. So, why do we do it, or rather not do it? I've decided that it's because it interrupts the creative process. We can't possibly create, if we are constantly stopping to write things down. Seriously though, take my advice and write down your patterns and those simple changes that you think you'll remember later, because you won't. It's for your own good. That is, unless you enjoy counting stitches or beads or tracing images from the pictures you took. If that's the case, then enjoy!