Good morning Olivier,
Before I joined the project, I understand that these options did something useful. (I can't define exactly what or when!)
As reported in bug 120538, they have not worked for some time, since the Help system was upgraded.
In Calc, the Help > What's This? option on the Menu bar appears to be available (not greyed out) but doesn't appear to do anything. Similarly the Tools > Options > LibreOffice > General > Help > Extended tips option isn't greyed out but doesn't appear to do anything.
In the latest Calc Guide, the text implies that these options will do something useful. The 6.0 Writer Guide gives the same impression and I haven't checked others. I am uncomfortable ignoring the fact that these options don't anything and running the risk of confusing readers.
Do we have an agreement about how cases like this should be addressed in the guides?