I just got a focusrite 2i2 and the sample rate was 48khz and everything was playing SLOOOOOWWW, so I changed it to 41khz and it fixed the issue. Why is that?

For some reason, your audio interface and DAW were probably working at different sample rates. That is, your DAW sample rate was 48000 while the 2i2 was working at 44100. So one second's worth of audio in your DAW (=48000 samples) would take more than one second (48000/44100 = 1.088 seconds) in the output.

There may be separate settings for these in your DAW's audio settings and the 2i2 driver settings, so you should make sure they match.

But yeah, like NP said there's not much reason to use 48000. Higher sample rates are needed in some processing (to avoid aliasing: https://en.wikipedia.org/wiki/Aliasing), but those are achieved by oversampling inside the plugins.

Of course, if you're Deadmau5 you can just say fuck it and work in 96 kHz.

Well, he is a mau5...

Of course there are benefits! The higher your sample rate, the more information you capture, the less antialiasing you encounter, and you could argue the cleaner the final signal sounds.

But if you're working in 96K, you'll find that anything recorded lower is either missing a ton of information or will just have a bunch of imperceptible noise added that might become perceptible after a bunch of processing. Inversely, rendering for publishing means you're placing a super duper steep high cut right at 22.05 kHz so it works on other playback systems.