I like the word "liability" you used here, because in Germany (where I've worked for the last ~5.5 years) there is another perspective of 'liability': an employer has to ensure that their employees take their vacation and adequately rest, else they expose themselves to legal liability. This isn't just about vacation - but also rests during each working day (I think it's 30 mins for < 9 hour workdays), and between working days (at least 11 hours between the end of day X and the start of day X+1).