If your sole measure of advantage is promotion then yeah, feel free to kick back your heels and do whatever you want.

Personally, I quite like to be doing useful work, and normal ramp-up times for people seem to be about 3-6 months, which if you work at a company for < 3 years can be as much as 10-20% of your time. More if you're switching between projects within a company. It's pleasant to not have to waste that large a percentage of your time getting up to speed.

I give new hires exactly one month to prove themselves now. I've found that giving more time does not increase the success rate of workers in any measurable way.

Here's a good example - I hired two admins within a week of each other. The second hire had closed more tickets in two weeks than the first one did in three. The first was gone soon after.

Not being effective sucks. Do you enjoy the feeling of starting somewhere new or starting with a new project and not knowing what you're doing? The trick is to minimize that time so that you can: a] feel effective b] not have a long term, negative impact on your team's velocity.