I just got a fairly substantial grant for a project from an external agency. However, as things stand, on this project I will not be the PI (primary investigator ) - that will be our head of dept. So why do I call it my grant? Because I wrote the proposal, handled all interactions with the funding agency, wrote the budget and arranged everything. My boss simply signed on a dotted line and shook a few hands. A symptom of the endless cycle of postdocs is that you don't have a permanent post until you're quite far on in your career. Therefore your own institution won't let you be the PI. The way around it is that you get a figurehead to be in charge, but you really end up running things.
This has its advantages and disadvantages. The big advantage is that you tend to have a fairly heavy hitter politically to back you up. He (and it's so often He that it's an insult to my female colleagues to pretend that they are equally represented) should have your back in exchange for drawing a fraction of his salary from your grant. The disadvantages are that you aren't officially PI for the sake of your CV - when you apply for jobs you are asked "Wasn't that X's grant?" when you talk about it - an it doesn't count as much for you. Likewise, they pay is miniscule. One of the things you learn writing a budget is just how much more a senior academic makes than a postdoc. It's depressing both how large the ratio is, and how relatively low the higher figure actually is.
Of course the whole process is a vicious cycle: You can't be PI, so you don't have PI positions on grants on your CV, so you have a hard time getting a permanent job, and so you can't be a PI... You just spend three of four months working on a proposal, sacrifice your dignity to the gods of the funding agency, ask someone else to take 90% of the credit, and prepare for hard work. On the plus side, you might just get paid enough to live and do what you love.