Different brokers have different rules. Some brokers allow...

Different brokers have different rules. Some brokers allow orders which are a long way from market / last traded price but they have to be authorised. So after placing the order, there's an anxious wait for it to be authorised before it's active. It's usually quick but still annoying - no last second orders. It might only take a minute but a minute before open is a long time.

There's definite advantages to having a second broker imo, even if the usage and cash held on that account are minimal.