let say that the combat system is same as Morrowind so so you can miss to attack
lower fatigue harder is to hit someone
well I think health should have similar effect
think you aren't exhausted but you're badly injured you almost can't fight
Well since attributes is folded into main stats, Strength and Endurance now represented with health and fatigue in more close relationships
Perhaps loosing health will decrease damage output in melee combat, while loosing fatigue will decrease weapon swing speed (so more heavy weapons what drain fatigue fast will have less swings) stat draining spell effects (magic, alchemy, diseases) will much more fearsome now,
I hope fatigue again have effect on magic and help for better concentrations during combat, so disturbed mage during channeling or charging will miscast spell, as well Magicka regeneration will be depend on current percent of maximum fatigue (like magicka don't regenerate if fatigue below 50% of maximum), so mages must stay full of energy to regain regeneration until will master something like combat meditation perk.