After watching the MARS series on National Geographic I noticed that they sent one of their crew members down a chasm to check for ice. I wondered, why they did not just take a regular commercial drone with them and explore the chasm with that?
Immediately after that, I realised, we have only been sending rovers to explore Mars till now (which was confirmed here). I think this is far too inconvenient to explore Mars. I understand a rover is more useful if you want to analyse the compounds in the surface of Mars.
Drones could cover a large area in a short time (depending on sunlight). Rovers have covered 40km max on their own:
If we are actually searching for present or past life on Mars, drones would come in way easier; they can fly right over large stones, (or into) chasms and other uneveness on the surface of Mars.
In my eyes, only energy supply would be a problem; however, this is solvable by landing the drones in sunny spots... which drones can find easier.
So, what's the deal?
Update (2018-05): NASA is sending a helicopter to Mars.