Mike, simplicity. In my case, a cast iron line going to an outdoor faucet goes right over my bench. pulling a single section of pipe, replacing it with two and a sprinkler head would be a 2-3 hour project. Depending on where the water is in another persons house, it might go from a simple tap in, like mine did, to a complicated session of pipe fitting that may run as far as 30 feet.
Flexible plastic tubing can be run anywhere. use clamps to hold it in place. You want to run the last 10 feet or so with metal, because plastic is not heat resistant.
i've done enough pipefitting with both copper pipe and galvanized that if I ever had to run anything but a straight perfect line, I'm going to go with flex tube. As it is, this 89 year old house does need some replacement, and that will be the way I go.