One valuable aspect of mentoring is the transference of institutional knowledge to new people. Technical skills are important, but learning about internal projects, past history/lessons, philosophy, etc are fairly critical for an organization to stay alive and survive through tough times.
Places I've seen that have zero mentoring also have zero transfer of institutional knowledge outside of osmosis and hubris (we train our people during our once a year 3 day meeting!). The end result is a few events can have a major effect. One senior person leaves and suddenly entire projects and systems are derailed and backlogged because no amount of technical skill can replace the knowledge of what actually went on in those products/projects in the first place.
