Two more reasons why it's a good idea:
First, many labs don't give a final water wash, just a stabilizer. This has implications for the long-term life of the negative.
Second, unless you pass by the lab on the way to something else, or use mail-order, doing it yourself is quicker and cheaper. My nearest pro lab is 100 km away in Tours; my nearest good amateur lab, 25 km away in Thouars; my nearest lab of any kind, 17km away in Loudun. In other words that's a minimum of 25 minutes each way, plus waiting time for the processing, and a minimum (for the round trip) of about a gallon/4 litres of petrol. If I'm somewhere there are pro labs handy, I'll use them -- I had a lot of film processed in Beijing, for example -- but otherwise, I do it myself.
Even if I don't use a kit to capacity, it still makes economic sense to process my own C41 and E6.
Cheers,
Roger