There are potential negatives to mingling money matters in one checking account, such as:
One person is bad at tracking checks, ATM or debit withdrawals.
There may be a feeling of a lack of autonomy and financial independence.
Some couples have a joint checking account but also maintain separate checking accounts. This joint account is typically used to pay household bills so all income goes into this account first. It is critical that spouses communicate well with each other to understand the monthly expenses, create a budget and ensure that amount of money goes into this account. Money, in the separate accounts then is typically either used to pay for the "wants" of a person and any pre-existing debts they might be bringing into the marriage.
