Do you ever have the (bad) feeling that you can't get into your car again with it so dirty? I do. My cars are probably not as clean as they should be but I do get to them on a fairly regular basis. Especially times after a trip or before the family goes on a excursion. You don't want to have to pick up the stuff that falls out of your car everytime you open the door!
Dog hair continues to be a popular reason for needing a detail. The hair sticks to the carpet and is plain old difficult to remove. I use a rubber brush to rub the hair off the carpet or seats as I vacuum. Also a dishwashing glove can work well. After vacuuming I blow compressed air to loosen the dirt and hair in the hard to reach places before vacuuming up again. It is a big relief afterwards.
I am asked to clean cars before a trip, making sure the windows were clean for perfect visability and the floors and cupholders were free of debris. I don't always get to clean the outside, but inside is where you spend the time driving so it makes sense to tidy up there.
Remember its easier to clean up afterward if you start clean and not dirty.