If you are only ever adding and never refactoring, aren't you already locked in? I guess supporting one piece of technical debt is probably going to be cheaper

If you are only ever adding and never refactoring, aren't you already locked in? I guess supporting one piece of technical debt is probably going to be cheaper than having to support a few legacy versions on top of the current version. However, the legacy version can at least be end-of-lifed eventually, whereas you would have to support all legacy features for the life of the product with the 'only add' method.