I believe the option to use the 'limits' of incoming Shore Power is to keep the Battery Charger from using too many amps when on 'less than' the full 'normal' 50amp 240v power supply. The Battery Charger is designed to use the full amount of amps it needs in order to charge the House Batteries... this is usually just fine on 'full power', but it you are using a generator or are plugged into 30amp or 20amp or 15amp shore power, the Battery Charger will continue to pull these same amps, potentially tripping the gen or shore breaker, because it doesn't 'know' you are on less than 50amp power unless you tell it...which is really what these 'limits' are used for.
When you choose 30amp, for example, the Battery Charger is then 'limited' to much less amps in order to leave more amps for your other usage, though it will take longer to charge the House batteries if you choose this limit, of course.
When you choose 20amp or 15amp, this is the same, and usually because that is the exact size breaker for the shore power you are plugged into, generally more like a normal 'household' outlet.
The 5amp limit is simply there to give you even another option - to almost turn the Battery Charger into only a 'trickle charger', usually if you really want much more of the amps for your own usage. Sometimes using the higher number will still trip the shore breaker, so the 5amp limit gives you even more control.
Of course, you probably even have the option of turning off the Battery Charger, all together, if needed.
...also, some coaches come with an EMS, or Electrical Management System, which is a automated 'shed' of higher draw devices when you are on 'less than' the full 50amp 240v RV Shore Power, or even on your onboard generator, which is also typically less. I don't believe that this is what your panel is used for, though, as your panel is an Inverter panel, which typically means you are changes settings for that device only, called 'Power Share'.
...2014 Ameri lite 259BH...
towed by our '14 Thor Palazzo 33.3 diesel pusher...