I'll be closing my browser soon anyway and they'll be gone
Sure, your browser cookie will be gone. But you have already allowed the server-side identifiers of your session to be used for whatever purpose, including reconstituting increasingly larger parts of your identity over multiple disconnected sessions. Please don't make the mistake of thinking that clearing your cookies afterwards is the same as rejecting all server-side processing.
Sure, but "rejecting all server-side processing" is basically trusting the website to honor my wishes. I don't put much faith in that at all.
They'll have my IP and browser fingerprint. Using Firefox mobile narrows me down to 1-2% of the world, but also lets me run ad blockers and noscript, to block some of the more troublesome trackers.
Sure, your browser cookie will be gone. But you have already allowed the server-side identifiers of your session to be used for whatever purpose, including reconstituting increasingly larger parts of your identity over multiple disconnected sessions. Please don't make the mistake of thinking that clearing your cookies afterwards is the same as rejecting all server-side processing.