And another point: it’s not really an “accounting standard,” but sometimes the reporting requirements imposed by the tax code are different from what GAAP requires (different depreciation rates are one example that springs to mind). Thus, many companies keep two sets of books: one for the taxman, and one for their financial statements.
As to the rest of the OP:
Usually when my clients (I am a corporate lawyer, doing mostly merger and acquisition work) don’t want to provide GAAP financials, what they really are trying to avoid is providing audited financial statements. An audit is an intrusive and time-consuming process. It is very expensive, and it means that key personnel are going to have big chunks of their time taken away from actually running the business.
In other words, it isn’t that GAAP in and of itself is onerous – most companies would, I suspect, generate financials in accordance with GAAP anyway; non-GAAP financials wouldn’t be terribly useful since it would minimize how well the financials could be compared to othe companies in the same industry. Your supervisor may be using “GAAP financials” as shorthand for “audited GAAP financial statements.”
Having said that, this stuff can get terribly complicated. The big question is classification: should a given outflow be characterized as a capital expense (and thus written off over time) or as an expense (written off in the current period)? How likely is a given potential liability such as pending litigation to occur – should it be reflected in the financials themselves, in the footnotes, or passed on altogether? Is a lease an operating lease or a capital lease? Do holdings in other entities need to be consolidated into the financial statements? Etc, etc, etc. Accounting, at least from an audit point of view, is less about mathematics (which is what most people think) and more about classification.
Oh, and one last thing (sorry for the stream-of-conciousness thing), and given you were practicing regulatory law this may apply: some industries, most notably insurance, have to provide statutory financials, with accounting standards prescribed by the state insurance commission (or whatever other regulatory body applies) of their state of operation. Those standards also differ from GAAP. Insurance companies usually produce both GAAP and statutory finanicals, though it is conceivable that they only produce the statutories; perhaps your boss wanted to avoid generating a second set of financials.