Using a non-default launcher gives you more options to customise your home screen and any other screens off to the side.

For example, Pixels always have the Google search bar right there on the home screen, and it's not removable (or not last I checked). But what if I don't want it there? A 3rd party launcher will usually give me that option.

Or another example - some launchers allow the use of gestures to activate certain things, eg open app A, start an email in app B, call a specific contact, etc. This can be gestures on empty parts of the screen or swipes on icons.

On my phone, on which I use Total Launcher, it looks like this:

Tapping each of those 12 icons opens a folder. But I can also swipe each folder icon up, down, left or right and have certain apps or activities open without ever needing to go into the app drawer.

So, if I want to make a call, I swipe left on the communications folder (top right). If I want to open Lemmy, I swipe right on the Internet folder (blue, bottom row). If I want to open my phone settings, I swipe up on the Tools folder. And so on.

That way, I can activate 48 different things while only having 12 icons on screen, keeping it quite neat and tidy, and leaving space for my little collection of widgets at the top.