All academic scientists worry about grants. In my weekly lunches with other faculty, that is often one of the first points they raise as a source of concern. I anxiously await now a score (if any) from my most recent NIH submission. Some colleagues of mine reported either euphoria associated with their recent NSF funding or sadness with recent NSF declines. Part of the worry is about keeping the science going that we want to do. Part is about not laying off good employees. But sadly, a big part is "image" to the university and to peers. Administrations (and often peers) ask frequently about how big particular grants are and then implicitly or explicitly rank the faculty member based on that amount.
We use dollar amounts of grant funding to assess faculty all the time: for hires, yearly performance raises, tenure and promotion, etc. Part of this is reasonable-- grant funding is competitive, so in an ideal world, someone who has good, creative ideas for feasible, high-impact research should acquire grant funding more easily than someone who lacks such ideas. Further, virtually no research is "free"-- one needs salary for themselves and their labs. That research may be subsidized by the university (as part of our "9-month" salary and TA-ships for students), but it's still not free. Hence, we need money to sustain our research.
That said, many readers will agree we've become too grant-obsessed in our assessments at all levels. New faculty members are immediately dubbed "successful" or "hotshots" if they acquire funding early, whereas early publication of high-impact research in a big journal often has a lesser effect. I recall once (I'll be vague for confidentiality) when 2 assistant professors were up for tenure simultaneously. One had multiple papers in the most premier science journal and multiple others elsewhere, and with a consistent publication rate along his years, but had acquired very little funding. The other acquired federal funding early but didn't publish anything until they put out a small number of papers in the year they were up for tenure (and none is journals as prestigious as the first). The faculty tenure vote was more strongly favorable for the second than the first, citing "sustainability" as a concern for the first.
Let me use an analogy. Funding is like gas to make the engine of research run. However, comparing faculty based on grant dollars is like comparing two cars in how far they'll go based on how much gas is in their tank. Many scientists are like Toyota Prius plug-ins (beyond from their interest in reducing emissions)-- yes, they need gas, but they can go very, very far with a small amount (~58mpg). Other scientists may be more like an 8-cylinder Chevrolet Camaro (~14mpg), or even a coach bus (~6mpg). There is even empirical evidence that very heavily funded labs, on average, produce less per dollar than mid-sized labs (ref).
Again, research isn't free, and sustainability is a concern, so we should not ignore funding. However, I will argue that IF we are to use grant dollars as part of a measure of evaluation, we should simultaneously consider that investigator's track record of "research efficiency per dollar" (like gas mileage). How many impactful new insights have they published per dollar? Shouldn't we be in awe of those who publish high impact work while using up less taxpayer money (and thus leave more for other research)? Shouldn't we consider research sustainability not just by how much you have, but how well you'll do in the inevitable situation in which you have little research funding? There are multiple ways to publish in PLoS Biology, Science, or Nature-- two are "scale" (you do something that's slightly creative but on a grander scale than anyone else has done before-- clearly expensive) and "innovation" (you come up with a truly creative idea and test it-- perhaps not expensively). It's time we spent more effort giving attention and reward to the latter of those two approaches, especially now when grant dollars are preciously limited.