Why a water jetter?
A water jetter is faster to set up, does a much faster job of clearing a blocked sewer, and usually saves time as usually no digging is required to gain access to the sewer.
How does it work?
High pressure water is used to cut and flush debris, such as roots, fats, sand, etc. The water jetter also causes a vacuum which can allow the operator to retreive at least a part of the blockage for inspection at point of entry. A good example of this can be found on youtube. A search of "hydrojetting - the chicken sandwich" ( a little odd i know) shows a great example of how it works.