INAL, but just to give one more example. If you're depositing >$10k cash into a bank, you (or your bank) have to report that to the IRS. If it's legally acquired, that's fine. However, breaking that same transition up into multiple transactions in order to avoid this reporting requirement is called "structuring," and it's a felony, even if the money was totally legitimate.
=> https://www.mybanktracker.com/checking/faq/rules-deposit-100...