Expense Accounts are used to help properly categorize your transactions inside Reconciler. These transactions and account details can then be shared with other accounting services.
Why you want to assign payments to Accounts?
By default, whenever a payment is reconciled with a PO, it will be associated with the COGS (Cost of Goods Sold) Account. However, it's a great idea to properly assign payments to corresponding accounts to track other business expenses whether they're recurring or one time.
*Example: Payment for "Microsoft Bing Ads" could be assigned to "Marketing" Account
How can I assign payments to an Account?
You can assign payments to an account in a few different ways. The first way is to take a single payment and assign it individually to a specific account:
How to assign a single payment to an account
The second way is to mass assign a set of payments to a specific account:
How to mass assign payments to an account
The last way is to have payments automatically get assigned to an account by having a rule created to auto assign once they are created in Reconciler:
How to create rules to auto assign payments to an account