Comment by gr3ml1n

Say you run a small ISP. You pay for (and utilize) a 10Gbps link to the internet from a big ISP: Cogent, maybe.

You look at your network traffic and notice 5Gbps of it all seems to be going to a single AS: Google. Your customers just love Youtube, and they are pulling down a ton of video.

Rather than leaving that as an interesting factoid, you decide to reach out to Google and pitch them on cutting out Cogent. You run a cable (more-or-less literally) from your network to Google. That 5Gbps of Youtube traffic is running over your connection directly to Google.

Now you can go back to Cogent and drop your commit from 10Gbps to 5Gbps, saving you a bunch of money. Google doesn't have to pay them for transit either: they can serve content to your users straight through the cross-connect. Win-win.

If a particular company is _really_ big, say: Netflix, Cloudflare, etc: you, as a small ISP, might even offer to give them some space in your server racks to host local caches. This makes the performance better for your customers, and, again: saves transit costs.