I work on a freelance basis and in addition to working more or less full time I am volunteering with an organisation partly to develop skills in a specific area but partly because I would like to'give something back'.
I have arrived at the office to find that nothing has been left for me to do by the woman supervising me who isnt in work today, WIBU to politely point out that even though I'm a volunteer I do have other things to do with my time if it isn't going to be used productively volunteering and suggest that I go home rather than waste my day.