From an ABC News story on AIG renegade executive Joseph Cassano, the infamous head of their Financial Products Division:
"Cassano set up some dozens of separate companies, some off-shore, to handle the transactions, effectively keeping them off the books of AIG and out of sight of regulators in the U.S. and the United Kingdom.
"'This is the other very important issue underneath the AIG scandal,' said Blum. 'All of these contracts were moved offshore for the express purpose of getting out from under regulation and tax evasion.'"
This is pretty much the point Mihir Desai makes in his work on taxes and corporate governance. Once there is a planning excuse for complex structures, they can be used for multiple nefarious purposes, e.g., tax fraud, avoiding internal and market as well as formal regulatory oversight, looting the company, etcetera.
Complex structures kill transparency. At the limit, they make corporate governance impossible and genuinely profitable activity by publicly traded companies a pipe dream. To some extent, this is a problem of financial not "real" activity, as the latter is much easier to observe. E.g., Apple Computers and General Motors both are presumably well-judged by the market because to a considerable extent one can see how well or poorly they are doing. But even companies engaged in real productive activity often have such large finance wings (think GMAC historically, or GE's recent problems) that the virus of non-transparency extends well beyond the pure banking and finance sector.