If you build lots of custom UI and animation, it's pretty hard to do it only with IB. E.g. with a custom component, you see a gray rect instead of how things ar

If you build lots of custom UI and animation, it's pretty hard to do it only with IB. E.g. with a custom component, you see a gray rect instead of how things are laid out, and you'd still need to write the custom bits in code anyway. Now you have the mess in 2 places. There's also other reasons like version control, being able to copy-n-paste, using constants, etc.