The HID drivers that come with your operating system work fine, but you’ll be missing out on any manufacturer-specific customization features (nonstandard buttons, remapping, DPI settings, lights, etc).

I also don’t tend to install software like that (including the GUIs for graphics drivers too—just install the driver through Device Manager) and I don’t care about the lost functionality. But if you want your fancy gaming mouse to have most of the special features it was advertised to have, the software is useful.

If you have a mouse with more than left, right, middle buttons and scroll wheel, it needs a 'driver'[0] of some kind so you can configure what the extra buttons do. Otherwise you can ignore the extra buttons and just use it like a normal mouse.

[0] I don't think it's an actual driver, I think it just remaps USB HID events from the built-in driver.

Nah. I'm on a Logitech 720 (bluetooth, wireless, many buttons) and didn't even know there was anything that I could download for it for Mac. It just works.

... but I don't care about customizing button behavior or anything like that, and only have a mouse this fancy because I wanted to 3-device switching on it (so I could easily use it on Windows and iOS, too). Though now that I've got one I'm kinda in love with the free-spinning scroll wheel and would have trouble going back to a normal one (though I hated it at first).

No, you dont. They work fine (at least my MX Master does) without, however you may loose some features like back and forward. Plus you need the software to customize settings like what button does what.