I wasn't sure if it was also never being done on a large scale in terms of individuals (e.g., if we never see Quirrell using Pensieves as a private training tool, or something).

As far as I know, the only suggested or shown uses of Pensieve in canon or MoR are (extrapolating a bit from Draco in MoR, and Dumbledore in both):

1. showing memories to another person
2. committing fraud or crimes
3. unburdening one's mind of many or strong memories
4. creating ideas & connections by going from memory to memory

The second suggests that the memories upon reviewing are just as good as a 'real' memory; the first suggests that they are convincing (otherwise why bother); and the fourth suggests that they are intellectually useful even if they were useless from a learning or skill perspective.