The point is how closely located data you access often is. If data is roughly sorted by creation time then data you access close to one another in time is stored close to one another on disk. And typically access to data is correlated with creation time. Not for all tables but for many.

Accessing data in totally random locations can be a performance issue.

Depends on lots of things ofc but this is the concern when people talk about UUID for primary keys being an issue.