No disrespect, I use offline Google maps almost daily, but there are far far better offline hiking apps out there.
Google will probably work ok for the most popular trails, and I guess you can use it as a supercharged compass. But at least in Europe, if you actually plan a route in any mountains based on Google, you're in for an adventure :)
Bit focused on eastern Europe, but has a hiking mode with very good coverage of the official routes (not only in eastern Europe ;)). And everything is free, including offline maps. Terrific value for casual trips.
Google will probably work ok for the most popular trails, and I guess you can use it as a supercharged compass. But at least in Europe, if you actually plan a route in any mountains based on Google, you're in for an adventure :)