[siffland]

I would guess in some positions, like those requiring clearances, that it is more important to have cleared employees there when needed than micromanaging if they are working 40 hours per week.

You wont keep most employees around for part time work, but you want to make sure if your production systems go down or customer orders need to be expedited, or an emergency patch, etc... that you have a team that knows how to do the work, can get it done fast enough and is cleared to do the work (if applicable).

In some cases it might be cheaper to have employees that might be idle a bit than to lose money on downtime. Just a guess though.