When everything in the system does what it should do well. Not subpar, half-assed, kinda-sorta or good enough. No. The idea of fully integrating something that doesn’t do everything well is so odd to me. Take Squarespace for example. The blog feature, while not like Wordpress is still more than adequate. In no way am I left wanting. Portfolio, pages, blog all in one place and everything does the job. Here I'm in for fully integrated. But if the main benefit of something is “well, it’s all in one place but this and that do kinda suck,” then that's not a benefit. When this happens, you should instead, always use tools that properly do the job. Or build them.