Onboard sound sucks.
My work laptop (Lenovo T420s) is useless for microphone audio (some Conexant chip). The company keeps wanting us to use Skype and Lync and SoftVTC to do meetings, but all the people who try to use the onboard audio are inaudible (because the built-in noise cancellation keeps ducking their voice), or if they manage to dig 5 dialogs deep to disable the noise cancellation (with an option that gets reset every reboot), they have lots of system noise over their voices (even if they're using an external mic. ). So everyone dials in via phone for group VTCs and mutes their PCs.
I have an expensive Jabra headset with a USB dongle. That gives me pretty clean audio. Should be able to use bluetooth too, but that takes more driver updates and even then it's still a pain.
My gaming PC has somewhat nicer onboard audio, but even with a S/PDIF link to my Logitech Z-560 speakers, I still get a hiss whenever the OS turns on and "opens" the audio device. Would be nice to be able to input digital audio somehow for Skype, but I ended up just plugging in a cheap USB webcam with a digital mic instead.
Still, it's kinda sad that any cheap mobile phone has a better microphone with AEC (for speakerphone use) and NC than you can get on most computers.