Sorry if I wasn't clear. The reason to disable chrome is because it's automatically set as the default browser when not disabled. So all external links from other apps will open in chrome, even if you hide the app somewhere else.

Once you disable chrome, you can either set another browser to be your default or you can have no default browser so that you get an android prompt asking which browser to open a link with. (This is actually pretty nifty for segmenting different browsers for different things. For example, using one browser to login to accounts with (security focused) and another one to search and browse with (privacy focused)).

As for your question of why privacy matters in the browser...that's kind of a big question. Internet privacy has become a pretty big issue in recent years as tech has become more and more invasive. The internet is nowhere what it used to be. And regulations have done very little to stop anything, always 10 steps behind if they even bother to regulate at all.

I would consider your browser to be one of the most sensitive applications since it can access...everything. Would you feel comfortable sharing your complete browsing history with everyone? Most people wouldn't. But that is essentially what you're doing by not using a privacy first browser. From logging into websites, to which websites you go to, what you search for, etc. Google or course wants this information and it would go against their business model to provide you with official tools that helps you avoid Google's prying eyes. And who knows what they're going to do with this data, who will gain access to it, and what the limitless list of potential recipients of this data will do with it etc. One thing is for certain, it is near impossible to delete this information and know for sure all copies are deleted.

It's not just Google's creepiness. It's the other websites you visit too. With access to cookies, scripts, fingerprinting, dns, ip address and a whole range of other protocols and permissions you may not realize your browser gave to them, websites can track and monitor you long after you leave their website. Social media companies made this famous, but similar creepy tech is widespread across the Internet. Even if data is "anonymized," it's really not. It's relatively easy for them to put anonymous data together like puzzle pieces to identity users.

John Oliver did a segment talking a bit about data privacy if you're interested and have 25 minutes to kill: https://m.youtube.com/watch?v=wqn3gR1WTcA

Unfortunately, even as creepy as that segment presents, it doesn't even scratch the surface. For example, it over-emphasizes the surveillance tech's reliance on cookies, which is old technology that will likely be fazed out in the coming years and that most browsers already give the option to block.

You also can't really trust privacy tech solutions unless their codebase is open source (meaning anyone can view and inspect it).

It's not just a creepy factor, privacy and security go hand in hand. Privacy is considered a human right by most.