Clear wp_postmeta files?

Hello there,

Is it ok to clear the files under wp_postmeta? Will it bring any harm to my wordpress system?

Thanks in advance!

Regards,
Kenneth

P/S: By the way, I’m not very sure what wp_postmeta’s is, but I read a post that says if we would like to delete unwanted stuff in custom fields, we could delete them from wp_postmeta.