This is also known as "research".
CRISP, the fore runner to RePORTER, was one of my best career guides as a newly independent investigator. I did a fair bit of grant snooping back then...and I still find it valuable use of my time.
For new faculty who plan NIH funded careers, this is an exercise in the necessary and the possible.
With respect to the former, sure, RePORTER does not tell all about a given PI's research support. You can't tell what participation there might be on other grants, funds from private foundations...or what fraction of her salary is on hard money. Nevertheless you can get an idea.
An idea of how various folks made it work, or are making it work, across their career arcs. I suggest starting with your own Department and then moving on to your closest subfield folks. Who do you think of as successful? Who struggles, in your opinion? Who turfed out in frustration over the grant seeking? Examination of their funding may give you some clues.
Admittedly the correlations will be loose. I've seen careers up through retirement that look like a long frustrating struggle to cobble together funding. Others where the PI disappeared (NIH funding-wise) mysteriously in the midst of what looks like good success. But with a large enough sample you can get an idea of how much funding you are going to need to sustain to have the career you are planning.
The *possible* is another interesting matter for your researches. We hear all kinds of rumors, conventional wisdoms and assumptions about the possible. Some of it backed up with data, some not. Much of it geared to career stage, where you publish, how frequently you publish, your subdomains of science, etc. These inputs create a sense in your mind about what is possible.
To land an R01 prior to a smaller R award. To carry two R01s in year 3. To renew a less than productive R01 interval. ....P01 or P50 BigMechs? How about a U or a contract?
When are you ready? When will study sections go for it and when will they not? Nobody wants to waste their time on low percentage efforts if the time is better spent elsewhere, right? So we strategize...often on mere rumor and old PIs tales.
I have usually found that the result of grant snooping is more encouraging than is conventional wisdom. Perhaps I am a glass-half-full type of person. When I see someone else having secured grant funding that appears to violate conventional wisdom, well, "why not me too?" says I.
I dunno. Perhaps it is a false comfort, but having some funded examples of whatever I am trying to do keeps my estimation of the odds out of demotivator territory.
It can also be comforting to review people who seemingly struggled on the grant shoestring for years before finally hitting it hard with multiR01 support. Perhaps this will keep your confidence up that things will eventually get easier. Don't forget to look at the funded intervals of support around renewal periods...there may be some gaps.
The point of this exercise is not to feel superior or run down other investigators in your field. The point is to reveal the feet furiously churning under the waterline so as to put the serenely swimming swan in context.
At the very least it should make you realize those other folks are naught but upjumped Ugly Ducklings... just like you.