Kneeling and Prone

[voodoo54]

After reading over the rules several times I cant figure out what advantage you would gain by kneeling or being prone. I see that being prone gives you a bonus to attacking with a crossbow, but that's it. Am I missing something? Why would you use these options in a combat situation? The only thing I can think of for kneeling is to maybe pick up a weapon? Any insight would help thanks!