I hate em. They make people write bad code and using them for interactive development is much worse than using a REPL. I cannot understand what people see in them.
It drives me nuts that some people see this as «either or».
Linqpad is another and different take on data-driven environments. As is various «SQL admin» alternatives.
If I don’t, the notebook quickly becomes bloated, I start getting paranoid about stale cells and lose track of what I'm actually trying to do.
Ideally the notebook’s sole purpose is interactivity, as kind of a quick-and-dirty frontend when it's not worth it to write an actual frontend, everything infrastructural gets moved out.
For interactive development, repl is a joke. Sketching out a fully working prototype of a few hundred lines of code (possibly depending on some data and context you don't want to reload) is impossible in repl.