Cuban - When discussing control in regards to the pop-up recovery, as in this part you have quoted, I am only talking about making sure the stick stays in contact with the ice at all times, the hands do not move any higher than where they need to be positioned in the goaltender's ready stance and the goaltender does not have to make any extra adjustments into their ready stance. Basically, if a goaltender is using a pop-up on a sliding save there should be little problem stopping inertia because the goaltender is now on the inside edges of both skates, assuming there is appropriate time to make a recovery into stance.
When talking about control and stopping inertia on a backside activation/butterfly slide there are a few factors that come into play. First, the goaltender must have strong visual contact to the destination target(where the goaltender is sliding to). If visual contact is weak a goaltender may over slide, taking themselves past the new position, which requires an attempt to stop inertia - which requires an opening of holes at inopportune times. Second, the goaltender must recognize whether it is appropriate to use a butterfly slide or a knee crawl recovery. If the space only requires a knee crawl major problems begin to occur. Lastly, control ALWAYS involves controlling the gloves and stick to make up for the opening of holes that is inevitable with all lateral movement, even a knee crawl. We tell our goalies to think back to some of the action figures they had when they were a kid. Some of the action figures such as the classic He-man figure below have a rotation point at the waste.
Control comes from understanding that goalies need to be able to control the upperbody (head, shoulders, hands, and stick) and lowerbody fairly independant of the other(just like the action figure above). A goaltender that cannot control the upper and lower half of the body independant of the other will have troubles opening holes which is especially a problem when plays are in tight and require a down recovery; or even a recovery to stance for that matter.
That is my best shot. Hopefully, this tackles the clarification you are looking for.