I noticed the little sear disconnecter (the little lever you flip down in the mag well to disassemble) was causing the trigger to feel real gritty. Anyways, I just installed a Apex trigger and sear and I left that stupid thing out. Is there any reason why I should put it back before I shoot it?
It's a M&P 9 without safety or mag safety.

Disregard.

Bin it.

That one pin in that housing holds the sear disconnect and the magazine disconnect ( mag safety).

I've been taking the entire pin out. I bought one of my M&P's with a mag safety to get a good deal. I had to buy AR15 springs to fill space left on the pin, to hold the mag disconnect to the side.

Then realized, the parts don't interact in any way other than their function, which isn't important to me.

My advise, take the whole pin out and all the small parts on it. Put it in a zip lock bag just in case. But leave the sear disconnect and mag safety (if present) out.

Unless you're a police officer. Then you must ensure that both a sear disconnect and mag safety is present. Also, ensure you are not near any Serpa holsters. Otherwise, you will end up shooting yourself.

This

Mine are all removed

Eta: though I wouldn't actually toss the parts.