I use to smoke pot untill recently (Gave it up due to either BJJ or pot) and it does have its advantages/disadvantages.
One thing i've noticed is some people get tense while rolling in BJJ/No-Gi but after a spliff you are more relaxed. Why is this a advantage? Simple as a tense person is much easier to manipulate (roll-over to get advantage posistion, Arm bar... Yada, Yada). I use to have a Spliff before training just to loosen me up as i use to be like corpse with a hard on (EI: STIFF).
Disadvantage though is lung campacity. Just like a Ciggie it lowers your lung intake by a severe ammount and this effect lasts for several hours (No brainer really) and same effect is with a Spliff. Your coordination is effected slightly (My reaction time was slower).
Silly question. Does a person with B.O offend you? If they do then if were ever in a competition together im not gonna have a bath for a month just to get advantage. :-)