Yes.  They are separate by default.

It is considered good practice by many Accountants and Bookkeepers (and therefore Accounting packages) to separate financial transactions into Journals by type of transaction (Sales, Purchases, Cash, Bank, etc).

This is to group related types of transactions together (to save people looking through many unrelated types of entries) and as a more efficient way of managing transactions when the work becomes greater than what one person can handle (staff can specialize by working on a single Journal or a small group of Journals).

In Odoo, Journals can have different sequences to number their entries, different currencies, and some can have default debit and credit accounts.  You can also setup rules about which accounts or account types can and cannot be used when posting via a Journal.  This reduces the amount of information needed to post a transaction, and adds controls to prevent the wrong accounts being used as you involve more and more people managing financial transactions.