I think it is, in the heat of the battle sheathing can cost precious moments that can decide on life or death (especially when it's about antidotes).
What I really hate is when the big monsters go behind load screen barriers so if I follow them I end up in the wrong area.
Never ever* sheathe your weapon when the boss is in your vicinity, even if you're on your last health point. Wait for the monster's next set of attacks to go past you, THEN sheath, THEN dodge the next set of attacks (unless the boss is distracted/panting), THEN head for the hills/heal. I rarely heal in the same zone that the boss is in unless it's on the other side of the map AND it's distracted, or it just finished an attack.
The extra quarter-second may help a bit, but you shouldn't be healing in a situation where that sparse amount of time makes any difference. The only weapons where the extra time may matter are the lance and switch-axe, which take a day and a half to put away, but the lance's shield and blocking techniques should buy you safety anyways.
*Exception if you're poisoned/on fire, but at that point you're pretty screwed anyways.
I'm trying to complete the Barroth armor to get some decent electricity protection for the fight against Lagiacrus but the only component I need now is 5x mud. That seems like it'll be hell to get. Barroth is so annoying to fight because he moves around so much (aimed for his tail? Sorry, he turned around so you hit his head and while you're recoiling he head-charges you for massive damage! Better luck next time!) even though I can now kill him regularly without any deaths.
Your odds increase greatly if you knock the mud off his flank, though it's not guaranteed even then. Also, don't aim for his tail! His right flank (your left if you're facing him) is his vulnerable spot. If you insist on cutting off the tail, get on his right flank, aim for his feet, and knock him down, THEN take out the tail while he's down.