Well, you can calculate how much money you would make in the time you do hobby, entertainment and eating. And I bet, “everyone” includes some people, that see setting up home/private IT not as hobby, for those people the comparison is like spending time x or paying amount x (data or/and money) (you could compare it to housekeeping) In such cases it makes sense to give the spent time a value in data or money, so that it is comparable

Maybe you spend time on selfhosting and now you have less time for other things that need to be done and now you have to outsource it (for money) giving time as well calculateable value