If your partner of not mature enough in financial matters then it is fine to have secret accounts for the benefit of both the partners. This will have a positive impact in long term till the time hopefully the other partner will be matured enough to understand. However if the partner has an inkling that there is a secret account then the purpose is defeated.
we always should keep some money in the secret ban accounts; usually one partner tends to spend on things of luxury & elevate up the life style; also now adays a lot of HDD & HDK's are around; we should keep money a secret