All of the Lights

[Ashawott]

Not as of Gen 3 onwards. Its to easy now tbh.

 

[Alec Empire]

I never use it.
The caves are pretty easy to navigate, anyway.

 

[psyanic]

I hate teaching any of my Pokemon to start with, and on the rare occasion I do, I have to go out and waste a team slot just for Flash. Screw that. I wing it and it comes out okay.

 

[Wings Don't Cry]

I used Flash in every generation except the first one because you could still kind of see everything on the screen. They didn't take the complete darkness thing as seriously as they did in Gen II where I found it was a necessity.

 

[Elite Overlord LeSabre™]

I tend to use Flash if only because I want to make things easier on me. The only games where it was a problem were the Johto games, as you need Flash fairly late in the game; in Blue and Leaf Green I hadn't assembled my full team of six by the time I reached Rock Tunnel and so I had a free slot for a Flash slave. In 4th gen IIRC, it became TM70 and it became easier to get rid of for a superior move.