[buro9]

If you're in short-term rental accommodation (1 year or less) or if you share a mailbox... then yes, these are concerns.

If you fail to respond to HMRC mail, you can be fined. i.e. missing reminders about a tax return, or PAYE info.

Both Companies House and HMRC will send authorisation codes to the registered address, and you can use these to change shareholdings, dissolve a company, make declarations that are untrue, etc.

You definitely need to trust the registered address a lot, and that trust needs to be stable.