I think the main concern which groups both concepts is 'usability'. I really don't know the reason why, but many sites seem to forget that concept. Whatever the intention behind your site is, you need to think about usability. If your site is not really usable, you will pay for it in the future; it doesn't really matter that you have a really cool design. If your site is not usable you are in big trouble.

So, when making a website or an app, you should ask yourself: is this the most logical and the easier way to do this? If the answer is no you should probably keep thinking and searching for a solution.