Is it worth spending the extra money to get the 1TB SSD option on a new MacBook Pro?
If you are using the MacBook Pro for video editing, music recording, or even managing huge quantities of hi res pictures in RAW format, etc. I would say that no disk is ever enough.
I had a 500 GB HD in my old MBP and it was always fulled up making the Mac slower and clumsy, I have to constantly move things to external HDs of 1 and 2 TB, so I will definitevely go for an upgrade in my new purchase, I wouldn't by a new mac to migrate all my staff and automatically find that the new HD is already full with my old stuff.
256 and 500 GB are not serious offers for a pro working with audio and video. 1 TB would be ok if you also have a few external HDs, 2 TB sounds the best option for me, even though it's more expensive, it saves a lot of time to have almost everything inside your Mac and not having to deal with many external HDs, searching in which hd is what you need, if they are USB or firewire now you will also need an adapter cable to convert thos to USB-C, etc. In conclusion, more time and more work.
But of course, if you are not using your mac to work and you are just an average user, 500 GB might be enough and you will save a reasonable amount of money.
Lastly, I dedicated small portion of my SSD to run native Windows version in case I like to play some computer game, which I honestly never done, but still want to have the option.