0000-07FF is RAM available for use for YOUR program. If you do a "STA $10" command, you won't be overwriting anything unless it's your own variable stored at that location.

Some assemblers might "hide" the actual address from the user by just having you define variable names (like "STA some_var" instead of "STA $10"). But once the file is assembled... all the variable names are just given a value to somewhere in RAM (0000-07FF range... or maybe the 6000-7FFF range)