theFooMart

I took around 1300 photos. Only like 300 of them are usable.

That's not horrible. Remember, sports is fast moving and can be unpredictable at times. This isn't family portraits or passport photos, you can't control everything.

Since lens with high focal distance are generally not that fast

Cheap lenses aren't that fast. Here's a 400mm 2.8 lens for $12,000 And if that's not enough here's a 200-500mm 2.8 for over $20,000

Even if you add a 2X extender that's still 5.6 at 800 or 1,000mm. That's not that bad when you're shooting in good daylight conditions.

And of course that's assuming you're shooting from a long distance. This is just one option to shoot wildlife. Another is to turn into a hunter. Camo, scents, lures, bait, blinds, etc. Combined with enough time and patience these people will get wildlife pretty close to them so they can use wider lenses.

I use it when the auto focus is turned off.

Seriously though, I do use it a lot. For example, if I'm shooting a hockey game. There's 16 players on the ice and thousands of fans. All at different distances. As good as cameras are, it doesn't know which person I want to take a picture of.

Or if I'm shooting fireworks or stars or something at night with a long exposure. In the dark the camera is going to have a harder time focusing on what I want because it can't see the thing I'm shooting.