Please re-read my comment. I acknowledge that both solutions have implementation and maintenance costs - which include the cost of re-training.
Anything over and above that _is_ waste.
(FWIW, I dislike the term 'training'. Someone else said this first, but I agree: training is what you do to dogs, education is what you provide people.)
I dislike the term 'waste' when referring to software licensing over 'free' software. As I said, it's not as simple as you are suggesting. I pointer out training (semantically, it is training), but there are other costs and factors to consider. I'm not suggesting for one minute that OSS is a bad choice, just that it is not necessarily the most cost effective in short to medium term.
Anything over and above that _is_ waste.
(FWIW, I dislike the term 'training'. Someone else said this first, but I agree: training is what you do to dogs, education is what you provide people.)