svegame works only when the game is exported?

Does the savegame works only when i export the game or also in the "development" state?

Both, however it is not recommended to load using saves from older versions of your project as they will not contain any new data you have added to the games since, thus when you load during development, you might end up seeing bugs that wouldn't be there if you were loading from a save from the same build.

What I tend to do during development is have it delete the autosaves I used for continue & new game on game launch. As for the default save system: use that at your own discretion during development phase.

Quick note: the save game files store data such as conditions, values, location of characters & various other things. So for example if you rename, remove or add a new condition, then you will have changed your games data structure.