In reply to henwardian:
Hopefully I can give some insight into this.
Worked for an energy supplier in the billing department inbound phone calls some years ago. We couldn't always solve the more complex problems there and then. Sometimes it required a systems expert, a manager, a different department. Most of which transfers don't have a direct inbound number, or extention. For example I couldn't just plug in a number and get exactly who I wanted. Or we might've been so busy the experts and managers were on inbound with us so had that to deal with.
If you were to ring back, there's no guarantee you'd get who or what you needed. So we'd leave a note for the person you needed to ring back because then at least the right person would be able to deal with what you need.
The problem is you're then relying on someone else to follow it up.
Then from the point of view of being handed a call back request. It wasn't always as simple as just picking up the phone and ringing back. Of course it helped if you had a well managed diary, and if requests were passed with the proper information (which they weren't always). We had to meet inbound targets, call time, off call times etc. making out bounds would ruin those targets as we were inbound. Seeing a huge que building, then not logging in to take another call but instead calling back on what was most likely a request with little to no information.
Manager call backs aren't all that easy, people tend to have the expectation that every agent has a manager sat behind them waiting to jump on the phone as soon as something tiny went wrong. Not true. A team of 12 had one manager, who had a lot to deal with and in busy periods call backs just weren't an option.
I've also worked on for a phone based fleet management company, dealing with vehicle breakdowns, services etc. there it was possible to direct transfer to an individual, but if they were on the phone, it ends up as a call back request. And we got mega busy at times, so often you'd get back from a dump and have a pile of call back requests to deal with. Those that seemed irrelevant, minor or had a lack of info on them would get binned. Too busy to do otherwise. If it was actually important, theys ring back and it'd get dealt with. Hopefully.
It's not ideal, and mega stressful. Personally I always felt guilty missing call backs, or passing on request that I just knew wouldn't be followed up. But it happens. Glad to be away from it all now!