Nothing really useful, you can see your demo playing in a different map other than the original one.
You will see people running in mid air, under the ground or outside the map.
This because players (and things) positions remains unchanged and maps have different ground altitude / dimensions.
Please note:
This does not work every time, some maps are incompatible.
For example, if the original map had no MG42 and you change it in a map with those turrets, you will get an error for missing weapon assets in demo playback.
