I think it's the programmers' choice to make the program run in full screen but we have to either wait for our requests to take effect or live with their choices or work around them.
Working around: My AMOLED screen (Galaxy S4) would burn in if the status bar was shown for too long while navigating and the fixed position icon on the screen would also burn in so I came up with a fix for each. Firstly I hide the statusbar with a separate free application called Status Bar Mini. I've configured this to only show a black band on top of the satus bar only when the navigation application runs.The second trick, probably the more effective of the two to protect the screen, is to use DayDream to bring up a black screen after a certain duration of inactivity, while the phone is under charge (which is the case when I use navigation). On battery the screen would go blank after a while but a phone's battery is never strong enough for a day long navigation. When starting the navigation program the car drive mode is automatically enabled and this would prevent DayDream to kick in so it has to be stopped (by touching it in the pull-down list of runnig applications).
DayDream has its own problems though in that it keeps the display on when closing the s-view cover while charging (screen burn in) so I canot leave DayDream on all the time.
So when I need navigation I have to do this:
Switch off the lockscreen
Turn on DayDream
Put the phone on charge in the car
Start the navigation program
Switch off car drive mode.
The effect is that the status bar is just a black band at the top (Status Bar Mini) and the screen goes black after a minute or so. The navigation program runs happily in the background and the voice guidance works fine. If the voice guidance is not enough and I need to see the map I simply touch the screen (lock screen is on None) which then goes black after a while of inactivity. When done with navigation:
Switch off DayDream
Restore the lockscreen
Slightly convoluted but this is the only way to protect the screen.
Suggestions to developers: make car mode optional, make full screen optional, make screen saver during charging optional. In general, although a niche goup of users, some of us need control of settings so they should be optional.