You would choose it for security hardening in general. E.g. it is harder for malware to infect, harder for unauthorized parties to gain access to data when the phone is locked, etc.

That and privacy, you also have a lot of control over what each app can do with gOS's permissions settings vs standard ROM and most of that is enabled by default. Can break some apps, especially banking related. I have 122 installed, of that three gave me a little bit of trouble where I had to disable some protections to get them functional. DeGoogled by default, I use microG for some limited Play services to get stuff like Youtube Revanced working.