Designing from top down may help you a bit when you already have a mental model that you'd wish to convey in written form rather quickly, otherwise risking to l

Designing from top down may help you a bit when you already have a mental model that you'd wish to convey in written form rather quickly, otherwise risking to loose sight of it when you get into details. UML helped me write down ideas (mostly communication flows and other behavior related aspects, not class diagrams), but I can understand why one may feel restricted when that's not necessary. Growing organically has its benefits for sure (is more fun, at least), but I also had more than one case of reconciling diverging/incompatible parts of a system simply because I went ahead of myself there with improvements on the go. Wasting time on that under deadlines is less fun.