Bottom right blue circle with icon of a road sign - right turn <↱>. It is quite useful button, it can show you also time tables for public transport near you. But I discovered it by accident so it is not that evident as most icons.

But usually if I want to search for directions not to or from current location I just search for destination and later just change current location to different thing.

What is missing for me is the ability to select time of arrival/departure for car navigation. It is useful to see how traffic is predicted to look like in advance. But you can get something a bit like this (with just enough advance) by creating event in calendar and using Google Now. It will notify you when you must go with taking traffic in consideration.

Thanks! Hidden in plain sight!

(For some reason it seems I only tried the search field and looked in the menu.)