1. It helps me understand the process end to end.
2. It helps the client understand his/her process end to end.
3. It makes it immediately visible where the problems lie thus helping both of us to create a solution for it (you cant solve something if you cant put your finger on the problem!)
4. We quickly figure out how many people are needed to execute the process and whether it is a proper reflection of what they are supposed to be doing.
So what is a Process Map or more importantly what is a good process map? People (mainly textbooks) define it in many ways and I wont bore you with those. In my own words, a process map is a dummies guide to doing something. If I create a process map using which my 80 year old grandma can walk through each step of the process and complete the task at hand, I have succeeded. As much as this may sound easy, it is not always a simple task. One might be too experienced in the process to create a map for it only because he or she may skip important things which are obvious to him or her assuming that the reader would already know them. Another problem with process mapping is incompleteness. When the process gets a little bit complex, several paths start to emerge and carrying through each path is important to understand where it leads!
I don't believe in re-inventing the wheel so here are some good links below which provide notations and basics of creating process maps.
What I would like to tell you is a few other things to remember when you follow the rules on the above links.
1. K-I-S-S (Keep it Simple & Stupid). Simplify. Do not use a single action box to show multiple actions. Fitting your entire process map on one page is not the goal. Helping the reader understand each step distinctly is. Also if your business process is a complex one, break it into logical parts and map them separately.
2. Ensure functional groups of steps are identifiable. What this means is that if your process involves multiple teams or multiple people, then ensure you are segregating and depicting who does what. Swimlanes are often very useful for this purpose.
3. DONT USE A COMPUTER! I usually work with brown paper stuck on a wall and post-it notes. Get everyone who is involved in the process to lock themselves in a room with you and map the process out. You can always draw it on a Visio diagram later on for review. Dont wait too long, post-its can fall off after some time!
4. Always keep the purpose in mind for which you are creating a process map. Remember, an account opening process map created for a customer doesn't need to include the part where the teller scans the application form, enters the details in the computer, makes photocopies of each page and stamps them as verified.