At what point PID and Odometry?

Here's a tread everyone can participate in. At what level of building do you switch over from simpler motion to PID and Odometry? or have you
made the cross over?
In my first robots, I used modified RC Servos. Later I went to encoded motors, and added PID. Then after that, I added Odometry. My minisumos are still modified RC Servos running open loop. Many of the larger contest robots were PID and Odometry based, to be able to do the job. My recent project for the Queen of Jordan museum robots were PI velocity controlled, without Odometry. My full size 3kg Sumo has encoded motors, but the software hasn't been done yet. My outdoor tank robot was fitted with encoders and (before it smoked) had PID and Odometry and I was just integrating GPS code in it.
So what are you folks expereinces? When you build a robot to do start with open loop design, or do you use closed loop PID, and Odometry?
At what point and what motivations does closed loop PID come in? Is it when you try to get your robot to go straight?
At what point and what motivations does Odometry come in? Is it when you try to get your robot to navigate?
Or do you feel robots start out fine without those complications?
Thoughts? -- Randy M. Dumse www.newmicros.com Caution: Objects in mirror are more confused than they appear.
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