The more experience I have had the more it seems like people won't know ahead of time what has to be done. So if there's a lot of planning involved without getting the thing to customers, there's whole a lot of speculation where 90% of the planning gets completely turned on its head anyway, when finally actual customers are able to use the thing.

And then slow builds and decisions would have to be rewritten anyway. Usually with many assumptions baked in.

So I highly prefer fast iteration where you get at least something out for the customers to use as soon as possible.