I thought the developer of the browser is the only ad provider that _doesn't_ need it (since they have other, better ways to get that intel which their competitors do not).
Also, it's very convenient in a work context if your employer uses G Suite/Workspace. I don't have anything to hide work-wise, and I do everything else in incognito windows.
that's the profile icon you see on your google-chrome UI.
but only fools use that feature.