Comparisons
Finger substitution--replacing one finger by another while holding the key down in order to free the first finger--requires much motion, more time, and a large key surface. As the substituting finger arrives, there is a risk of striking an adjacent key. As the first finger releases, there is a risk of releasing prematurely and causing a re-strike of the key as the substituting finger arrives.
On the other hand, finger substitution is instinctive--but this is precisely the downfall of the technique. It is often used when fingering has not been well planned; that is, when one of the other more efficient techniques ought to be used. However, when there is adequate time to execute a substitution, and when it can be executed cleanly, the technique is indispensable.
