I dug up this old thread. Some of the discussion addresses your question.

http://www.airlinepilotforums.com/ma...tml#post430326


Here a few excerpts:

I have to disagree that picking up open-time and VJMA does not affect staffing levels, especially as any company moves towards furlough. Though I am not privy to management’s exact methods, I have to imagine that they use historical data in their future projections- i.e. in the past they needed ‘X’ amount of pilots to cover 1,000 hrs of block flying, it is likely that they will make plans based on the assumption that future needs will be close to that ratio. Every pilot that picks up open time and/or VJMA willfully validates management’s assumptions. Why staff the company properly (and keep guys/gals off the street) when all or the vast majority of the flights operate as scheduled?
.....

Then there are some that were saved by age 65 who are picking up open-time/VJMA for important (to them) projects such as upgrading their motorcycle, boat, significant other, etc.- Inflict wound and then generously pour salt.