Many would say that that's a good thing. In some ways perhaps it is, but on balance it is mentally draining. It's particularly taxing on the brain because I write mysteries.
When a new idea comes along, I have to do a flashback with what I've written so far. Does the new scene/new character/new bit of dialogue fit with what I've already written? (Yes, I know that what I've said thus far applies to all writers and all genres, but just wait...)
When it comes to parceling out clues in order to play fair with the reader, making decisions and changing your mind presents several challenges. It's like playing a game of chess with a master: forecasting their moves, computing what moves you can play in response, and figuring out the implications of putting your Queen here or your Rook there.
Let me give you an example:
I've just revised a chapter for the next Sasha Jackson Mystery and the chapter presented a lot of challenges to me. Each revision would alter the course of the rest of the book. A certain character - with ties to the victim - came across some potentially damning evidence. But said evidence may relate as well to a crime that's unrelated to the one Sasha has been hired to solve.
If that piece of evidence is turned over straight away to the cops, that's fine... But then A, B, and C can't happen because Sasha won't know/have access to that piece of evidence.
If Sasha gets that bit of evidence holds onto it (even for just a little while), then that's fine as well, but it will mean that X, Y and Z will need to happen as a result of her having this piece of evidence. It will also mean that characters Q, R and S won't be motivated to act or react until the evidence is finally shared.
As I played either choice forward in my head, I could see advantages and disadvantages to both. I could make either one work, and each could ultimately lead to the conclusion I want, which is for Sasha to solve her case.
Other choices I've had to make along the way relate to things like transportation. If a character is on the (Toronto) subway, then they can't receive a phone call when I need them to because there is no cell reception on our subways. So, I have to go back and change it so the character is riding a bus... Or maybe the phone call happens later... or maybe it went straight to voicemail (because of the lack of service) and the character didn't notice the new message until later.
But if they DID ride the bus and DID get that strange phone call asking them to go to a clandestine meeting in an alley with a mysterious man, then...
But if they DIDN'T get that phone call inviting them to meet with that mysterious man, then what would they have been doing it that alley... and how did they come across that bit of information? Or wait, maybe instead if they... You get the picture.
Sometimes I think I should write down all my ideas, all the plotlines, and all the clues on little index cards, throw them into a hat and just build a story around whichever ones I draw. Or, I should ask a chess master to be my sounding board.