If you're applying for a mortgage, the lender will almost always require bank statements from the past few months. The lender uses these statements to verify your income and track your spending habits.
There are a few exceptions when bank statements aren't required. For example, if you're self-employed and have multiple sources of income, the lender may instead ask for tax returns or profit and loss statements.
In general, it's a good idea to provide bank statements even if they're not required. This gives the lender a more complete picture of your financial situation and can help strengthen your application.