While you can save Google maps offline for using it without internet, they have own set of limitations
Offline Google maps miss certain feature
Certain features available in Google maps online cannot be used with offline cached file viz : 3D buildings, indoor maps, satellite and terrain view.
Directions and Navigation not available offline
Since these service requires internet they cannot be used offline. However remember that Android GPS don't need internet and hence navigation may be used on offline Google Maps once you get the track route.
Offline Google Map cache size
While Google allows you to save Google maps offline, it has file size limitation. If you try to save large area, Google map will show message The on-screen map area is too large, zoom in first. Google does not describe the exact file size or parameters on this restriction, but perhaps size depends upon the layers of data in the map area e.g. Open fields and sea areas have less details so perhaps large geographical area can be cached offline but city has clustered details as you zoom in so less area is cachable.
The max cached file size was about 4.5 to 5.0 MB which I was able to download. I read somewhere that Google does not allow more than 7 offline cache, however I tried 9-10 times without problem. Due to this restriction, larger Map areas need to be cached in parts .
Offline Google Maps not loaded directly
I was unable to find any option to load the cached file directly in the Gmap. If you try to search in offline mode you get error No network connection. If you do not have World map loaded when you open maps then I think you need Internet in the beginning to get map of concerned region (zoomed out). Once you have that, Google map smoothly uses your cached file to get more details as you zoom in.
GPS location may get delayed
Your GPS uses internet to perform better and reduce TTFF (time to first fix) so that it get your position fix faster however internet does not affect its accuracy. So while your Android phone may delay in determining your position fix without internet, once found it will work perfectly indicating your device as "blue dot" on offline Google map
Please let me know of other limitation if I missed some or you faced while using Google maps offline.