Tricky one. The circumstances can include:
The bank made a payment without the correct checks that the funds were available. In essence, they can get the money back to cover the bank's own interests.
Unauthorised payment (without the account holder's permission).
A mistake in the account details (paid the wrong account).
A mistake in the payment amount (eg. paid £1000 instead of £100, etc.).
It is suspected by the Bank that the funds within the outgoing account may be subject to being reclaimed by another bank/account or the courts/police. i,e. placed there by dodgy cheque or suspect debit card, etc.
It is a much safer means of receiving funds due to the limited possibility of a chargeback, which credit cards and e-money companies (like PayPal) are subject to.