How important are fatigue rules?

[weby]

I tend to ignore the mundane FP things(sleep,food,travel etc) in situations where they are nor specifically the plot point.

But as said by Kromm they are the "Hero fuel", players regularly use Feverish Defense and several other similar options. The running low on FP is one of the big limits on combat endurance in our games as in the +2 is kind of a big deal often in avoiding the downward spiral in damage.