How do simple queues work and coexist alongside Queue Tree in RouterOS of MikroTik devices?

Basically we have created both Simple Queues and a Queue tree and wondering a couple of this:

  1. will cause any weird side effects?
  2. Is this is an antipattern ?
  3. we should do everything with Queue Tree ?
  4. how will the two get prioritized between each other anyway?
    Any other share of your past experience with similar setups would be appreciated
    Many thanks