Many banks in Thailand will request a valid work permit or a letter of residency of your address in Thailand from your respective embassy in order to setup a simple saving or current bank account. These documents do help expedite the process and open up the number of banks that you can work with.
While other banks will only request the original copies of your passport, original lease agreement if you are a tenant or an original sales and purchase agreement if you are an investor of a property.
A bank account is not actually required to buy a property here in Thailand. You can use a lawyers account and/or transfer monies directly to a developer. If you plan to receive rental from your tenants locally, having a bank account surely helps. It's also super handy to have access to local funds and local transfers through bank Apps making it easy to transfer odd expenses when overseas.