The Interactive Brokers U.S. Microcap Stock Restrictions page says:
Execution-only clients (i.e., execute trades through IBKR, but clear those trades elsewhere) may not trade U.S. Microcap Stocks within their IBKR account. (IBKR may make exceptions for U.S.-registered brokers)
How is it possible to execute trades through one broker, but clear the trade through another broker?
When I buy a stock through an online brokerage, I don't see separate "execute" and "clear" steps. Instead, I just click on "Buy" and wait for my order to be filled. Under what circumstances will I need separate "execute" and "clear" steps, and why would I ever need to clear trades through another broker?