Grant finances can be complicated. If your institution is anything like mine, even the mildly complicated initial budget gets a bump of ridiculousness when it hits the university coding system. Suddenly some categories are lumped together while others are split, with no apparent rhyme or reason to which is which. It's taken me long enough to figure out the intricacies of budgeting NSF proposals, but spending the money is an adventure in itself. Luckily we have very competent finance people to marry the proposal budget to the uni system and make the money flow.
But the mechanics of spending off a grant are hardly the only complicated factor. Another issue is how lines between projects blur when it comes to the flow of money. I know granting agencies want you to dedicate every penny from a grant to only that project, but I also think they recognize that science doesn't work in a linear fashion. Many projects have overlapping aspects and we are always trying to do more than what we wrote about two or three years ago as technology changes and new things become possible.
Put simply, grant budgets are flexible guidelines.
Given this, I am curious how forthcoming most PIs are with providing budgets to their trainees. Personally, I have never had a problem giving anyone working in my lab the full proposal for anything we are working on. My reasoning for this is two-fold: First, I think it useful for those hoping to make a career of this to get a feel for how grant budgets work. Where does the money go? How much do things really cost? Second, I think it is helpful for people in the lab to see the personnel costs. It's easy to see a big number on a funded proposal and think they lab is rich, but dig deeper and once you take out the university's cut, people are what drives the budget. This is generally under appreciated.
One of the drawbacks of doing this, however, is that people tend to view a grant budget in a vacuum. When you are thinking about a single project and have the budget in front of you, it is easy to forget that the budget is just one piece of the lab puzzle. There are many other factors and it is not as simple as it appears in the budget justification.
As an example, my university does not cover summer stipends for graduate students, leaving this up to the PIs. I don't believe it not paying my people over the summer (yes, some people think it is fine to pay only the academic year) so I have to make sure I can cover everyone in the summer. We also have a unionized grad student body, and the union sets academic year pay scales, but only has limits for the summer. Oddly, however, there is Summer Pay and then an allowance of "extra" summer pay in the union contract.
When I wrote up my budget for our grant, I maxed out the summer pay category, including the full summer pay and the "extra" pay money. Looking at the project in a vacuum, one might assume that I intend to pay the student on the project very well (by grad student standards) over the summer. But in reality I intended all along to have the "extra" pay be available to cover the partial summer stipend of another grad student, whose project isn't federally funded. Summer stipends can be tough to cover, but here is a mechanism to ensure more students are paid.
Based on this and other shell games that sometimes have to be played with grant finances, I'm not surprised when I hear about PIs keeping their people in the dark when it comes to lab budgets. I would be curious whether anyone has seen any bad consequences to being open about finances.