There is one basic reason for routine maintenance (i.e. pumping) of your septic system.
REMOVE INDIGESTABLE SOLIDS.
As explained in "How a septic system works", the septic tank is a solids collection system. The more solids it collects, the less efficient it becomes, and the more solids are passed with the effluent to the drainage system. As the tank becomes overfull with solids, the tank may plug (thus backing up sewage into your home). Also, the amount of solids retained by the tank is reduced. Thus sending damaging/clogging solids to the drainage system.
If you just wait for the system to fail (back up in the house) you run the risk of costly drainage system repairs or sewer hook-ups (if available).
While the tank is open, your septic system should be inspected for damage (concrete corrosion or baffles missing/corroded) or impending drainage system failure.
We use a digital camera to inspect the inside of your tank (even on deep risers) to provide you with the best assessment of current conditions. This also gives you, the homeowner peace of mind since you can see for yourself!