No Butter Sous Vide: What did they mean by this? I just watched an experiment on youtube, where they compare 2 steaks, side by side, the first one with added butter during sous vide (as many people do), the second one without butter.

It seems the second steak, without butter, was far better, and I have since read other sources suggesting to sous-vide without butter or oil for best results.

However, what should you do when searing? Should you also avoid butter there, or is butter OK, when searing? What about oil?

What about the advice, often mentioned, that if you put in herbs during sous-vide, you should add some oil in order to get the essential oils out of the herbs?

Source:
https://www.youtube.com/watch?v=hNtqr8x_u7I
The (alleged) problem with extra fat during SV is that, flavor molecules will dissolve in fat and subsequently be discarded. 
The claim is that, this causes the loss of flavor.

For searing it’s fine to use butter or other fat.