I work concurrently in a large company (45,000 employees) and a small company (50-ish, but for years we were in the 5-8 range). I am solidly convinced that the larger a company gets, the higher the number of excess employees.
How do I work concurrently in both companies? My primary employer is the small company, but the large company has subcontracted me via my primary employer to work in their HQ 3 days a week because a specific department (which my primary employer specializes in) is swamped, or so they say. So, 3 days a week I work at the big place with very little to do and end up doing a small amount of work and lots of web browsing or reading or working remotely as I'm able on tasks for the small company. And then 2 days a week I'm at the small company, swamped and playing catch-up.
Granted, this is but one example, but the contrast I see on a daily basis is stunning. Even in my smaller employer I see us getting more inefficiencies and "dead weight" employees. Back when our employee count was in the single digits, it was a whole different ballgame. We were small. We didn't have the resources to carry extra employees. When someone would quit, it was a huge deal because we'd be losing literally like a sixth of our entire workforce. And it was a fun environment! It truly felt like a tightly connected team.
Don't get me wrong, I'm not complaining. I've been employed at the small company for 16 years and have no desire to leave. But to get back to the original question, the bigger a company gets, the more dead weight they'll carry until the times get really tough. Then, you'll see where they can cut the fat.
Here's an example. A few decades ago, the Rock Island railroad was a well-known railroad across the Midwest. They went bankrupt in about 1980 if memory serves. Leading up to their insolvency, they ended up leading the industry in getting down to a 2-person train crew because they simply had no money to pay additional crew members. From what I've heard, managers literally told train crews "Tough luck, you get an engineer and a conductor because we can't afford to pay for a brakeman." And now the industry standard is a 2-person train crew.
Aside from Microsoft, a FAR better question would be (not to turn this political, but it's a fair question): "How many employees does $government really need?"
Where am I going with this? I'm not sure. Maybe I'm rambling because I'm bored. :)