Question: Are there situations in which a pilot could/has to lower the landing gear during flight for reasons not directly connected to landing? (i.e., not part of the landing checklist)

Originally I thought I had seen some around the location indicated by the pin on the map below (17° 25' 30.093" N, 78° 32' 27.4734" E), in the evening time around 4:00 and the weather was clear.

[![Sighting location](https://i.stack.imgur.com/78nOO.jpg)](https://i.stack.imgur.com/78nOO.jpg)

Answer: 
That's **nowhere near midflight**. You are seeing aircrafts approaching [Begumpet Airport (VOHY)](http://ourairports.com/airports/VOHY/)'s runway 27. This airport has no airline service, but it is used for some general aviation including VIP flights and as military airbase.

The point directly north (about 3 km) from the coordinates you gave ([N17° 25' 30", E78° 32' 27"](https://www.google.com/maps/place/17%C2%B025'30.0%22N+78%C2%B032'27.0%22E/@17.4532706,78.5342887,13z/data=!4m2!3m1!1s0x0:0x0)) is about 6 km, or 3.2 nm, from threshold of VOHY runway 27. Given usual 3° glide slope the aircraft would be just about 1000 ft above runway elevation, which happens to be the latest point where landing checklist should be complete. Yes, that means gear down. It also means it will be touching down in about a minute and a half.
Yes. If you want to increase drag to lose altitude quickly. For example, mountain flying, need to descend rapidly and speed brakes + flaps just aren't cutting it.

Fun fact: The F4U Corsair used its landing gear as speed brakes. There was a special way they lowered them in this case. (I belive the hydraulic struts weren't locked ect., so landing on them would not be smart)