Do cold emails actually work for getting a postdoc in the U.S.?

In the U.S., how common is it for a PhD advisor to introduce their student (via email or in person) to a PI who has a postdoc opening? In some countries, getting a postdoc position heavily depends on these introductions, but I’m wondering how much this applies in the U.S. as well. Is it a major factor, or do most people just apply cold?