When I worked as a inbound call centre operator in the early 2000s they used to measure your "productivity".
Productivity was the percentage of your work day that you were busy on an inbound call. The problem with this was that when you call a client back, that call wouldn't be counted towards you productivity. The other problem which is relevant to this is that when you do a large number of calls (keeping your calls short and concise) the time gaps between the one call ending and the next one starting added up quicker for fast workers translating to a lower productivity. (I should mention that a large part of your bonus was calculated from this "productivity").
So if you answer a call and you can keep that call going for as long as possible, your productivity would skyrocket. On average the number of calls per person dropped on average from roughly 150 calls per day to 90-100. (anecdotal, but I observed my teammates)
This is how I got fired. (greatest thing to ever happen to me btw) I didn't like talking to people, but I was a dumb 20 something and had no other options, so I would answer the call, with a double tap, that would put the caller on hold immediately and I would just hang on to the call for as long as they stayed on the line. The other way was to start the call, get the info of the client and then tell then you will check with whoever and then just leave them on hold. For the case that got me fired the guy was sitting and holding for more than 7 hours.