You asked a really good question
I do like the design process, but since I use EQ5 and have a limited stash of fabric, sometimes that process can be frustrating because I can see it in my head, but getting out into the software is another matter entirely. It was by chance when designing my sister's quilt that I came across the kind of fabric I really wanted to use, then it seemed like the clouds parted and the angels started to sing.
Truthfully, I'd have to say the troubleshooting aspect is what I like the most. I know that sounds weird, but when you're working on a block and it's not coming together correctly, so you work on it again, and maybe this time, it still doesn't come out. So then you work it a third time and suddenly, there's a light that comes on and you see what you've been doing, so you tear the block down, sew it again and it's perfect, that's when I feel the most accomplished. That's when I can start to whiz-bang blocks out like a factory and I'm grinning from ear to ear while I'm doing it.