Its like a water valve, even if you crank it till the valve breaks off, its still going to be water coming through it.
Simple really. No gates open, you've your "normal", restricted flow available. You can do big jutsus but they're taxing as expected because you're far from your max potential. Kind of like forcing a giant piano through a tiny doorway.
Then if you open gates, the more you open the stronger your flow becomes. Open the floodgates, break off the valve, remove the funnel, whatever comparison you wish to make, same concept still. Your body nor spirit don't change so it is still the exact same chakra as you mixed before, you just have access to more of it from your total pool at once, instead of a slower dribble. Potentially significantly more so, considering with 6 gates Gai was pushing a giant water body back with sheer chakra alone, and with all 8 he made a colossal dragon that obliterated half of a 10 tails hosts body in one kick.
So you open gates, what then? You can be Lee or Gai, keep it inside the body and use it to boost your physique to ridiculous levels for epic taijutsu. Bijuu chakra can achieve a similar effect too if its not used for jutsus, as seen from Naruto even before he ever achieved even a 1 tailed cloak. He went from a shrimp to overpowering Neji.
Alternatively you can utilize that greater flow for jutsus. As expected with more gas to the flames, you can run out much faster, perhaps even burn yourself (or network in this case) while at it, but its no longer meager flames but a bigass bonfire instead.
As for how this would come into play with susanoo, like I said it won't do squat about your apparitions speed, that will still be dependent on your skill/control and that alone. It should in theory however make it a fair to significant degree easier (depending on gates open) to form the apparition however, because you're no longer tearing your body to pieces trying to rip out all that power, you can just flood it out instead.
