What are your usage patterns?
I've found 256GB to be a bit of a sweet spot. I can't get everything I would ever want on the disc, but it's enough with maintenance and uninstalling things I'm no longer using to any great extent. And the performance advantage of an SDD is so ridiculously nice that I would never give it up for a bit of extra convenience.
If you're doing things that are seriously space heavy like video editing, you'd probably need an external storage source to make up the difference. But for coding and general use, I find it to be more than enough.
Saying that, I'm sure there are developers out there who couldn't live in 256GB. I'm not sure how common they are but I'm sure they exist.