S.H.
Many moms (and dads) prefer to have a doula in the role of labor support and coach.
I have to consider this in the event that my folks aren't here in time to care for my toddler (we have no real good viable overnight babysitting options). I plan to have a back-up doula and midwives to help me through the process.
Some husbands prefer that a doula take over the coaching aspect of labor because they are not comfortable or confident to take that role (unless they've taken a Bradley Method class, etc.). Some moms prefer it as well because the doula is knowledgeable and usually very good at easing labor (as well as helping to prevent cesareans). Some are more expensive, some are more experienced - and some are fresh out of classes, so they are free.