True for PhD applications as well. A honest and informed explanation of why you apply to a few selected labs will get you further than sending the same copy/paste message to a hundred random places...
What's the most important factor in post doc applications? Is it the number of papers? Where you did you PhD? No, it's how you write the email. More specifically, you'll get a reply only if you take the time to write a personal email & explain why you apply to this particular lab