You'll get the most benefits out in the weight room out of season. During season, specific exercises like the sprints mentioned will most likely benefit more.
Think of it like a car. During the off season you might put in a bigger engine (hypertrophy) or make the engine more efficient (get stronger for your weight). In season you are making final tuning adjustments to get the best possible racing times (speed work). This is not to say you can forget about speed work entirely during the off-season, but a larger focus should be on getting a more efficient engine in my opinion.