Any professional in any industry will tell you that the key to success is the communication of information.  Your business needs a way for your employees in the field to effectively communicate with your employees in the office.  A way for the guys in the field to quickly and accurately clock-in/clock-out of a job, note the actual amount of material installed, send recommendations back to the office that could result in additional revenue from your customer, upload documents and pictures, and have a place to add any extra expenses they might have incurred while in the field.