Forgive me raising a tangential issue: the aforementioned use of landing gear as an air-brake - considering the limited efficacy of air-brakes (sorry, "Speedbrakes"). Extending the gear was remarkably effective on all the jets I flew. Particularly, of course, during gear transit, when the doors were open. Unless ATC had presented you with a near-impossible "go-down-slow-down" requirement, however, there was a feeling of having screwed-up. Because it was such a rarely-used expedient, it was quite difficult to judge how early to do it without over-kill. Subsequently, one could end up having to drag the a/c on to the approach with a lot of thrust, adding to the general noise and vibration. To make matters worse, sod's law sometimes involved ATC taking you around a leisurely circuit to fit their congested pattern. The dilemma then was: shall we raise the gear temporarily? Reckon I only saw that done once during over 30 years on jets. There seemed to be an unwritten taboo on it, and from the 1990s we were contemplating some sort of flag being raised on the post-flight QAR analysis (such as SESMA).
As with slats and flaps, obviously we have to be aware of the fragility of gear doors operated close to the limiting speeds, but would the occasional cycling of the legs themselves represent a problem in terms of wear and tear? I'd be interested in the comments of pilots and engineers on the above.