DAE - Put Thermal Paste on the CPU and then place it on the motherboard?

Just wondering. I've been spending a lot of time on BuildAPC and I've noticed that a lot of posts from users of differing computer building experience, as well as a lot of online guides, put a CPU in it's socket first and then apply Thermal Paste to either the chip or the heatsink.

When I was taught, many years ago, how to put my Pentium 3 800 mhz computer together, I put the thermal paste on the CPU in hand before placing it on the motherboard.

Is this just all personal preference? or is there a logic behind placing it in the socket first. Just wondering.