Limit Switches

Do i have to have limit switchs? I don't have any on right now
and every time I run a program it starts in a different spot. Even
when I zero out all the axis's. It should do the same thing every
time right? I am using Kcam. Also can I home my machine with out
limit switches? Every time I go to home it head in the opposite
direction. Building this machine was the easy part, learning the
software is the hard part!!!!!!!!!!!!