You use the future tense when to events happen in the future, regardless of their durations. For example: "Quand je serai vieux je vivrai à la campagne." Now let's make this into a bit contrived example using le futur antérieur: "Quand j'aurai vieilli, je vivrai à la campagne." The first example concerns two points in time: being old and living in the countryside. The second example is different: "when I will have aged" refers to the end of a process. Hence the futur antérieur. -- Chris (not a native speaker).

By the way, the example given in the lesson "When I have finished my work I will watch TV". This is, in fact, improper English since in English as well one would need to use the future perfect tense: "When I'll have finished my work I'll watch TV". -- Chris.

Chris, it is proper English, at least in the U.S. I've never heard a native speaker say "when I'll have finished my work ...".