User can activate this module's functionality by configuration from Path : Accouting > Configuration > Setting.
User will find here a option --> "Show Recent Transactions On Invoice/Bill Validatation ?"
If user Activate(tick) here, User will find a pop up for vendor-bills or customer-invoices transactions summary while validating draft Bill or Invoice.
If user do not activate(Untick) here, pop up will not open and bill/invoice will be validated as default odoo functionality.

Let's take a example for Customer Invoice.
Here we can see total 7 invoices of Agrolait. Lets validate a draft invoice which has invoice date 09/15/2018.
Refer below screenshot.

Now Open a draft invoice and Click on Validate button.

After clicking on Validate button, Pop up will be open where we can see all invoices of Agrolait(without current draft invoice).
Details of Invoices:
1) Customer Invoice : Number of related Invoice.
2) Invoice Date : Invoice Date of related Invoice.
3) Due Date : Due Date of related Invoice.
4) Total : Total amount of related Invoice.
5) To Receive : Receivable amount of related Invoice.
6) Currency : Currency name of related Invoice.
7) Status : Status of related Invoice.
8) Source Document : Source Document of related invoice if invoice created from Sale Order.

By Clicking on Validate button from Pop up screen(Wizard), current draft invoice will be Validated and Its status will be change to "Open".

When Accountant validate a draft invoice and not found previous invoice of related customer, Below messagae will be show in Pop Up screen and simply Accountant can validate from pop up screen.

Let's take a example for Vendor Bill.
Here we can see total 7 bills of ASUSTeK. Lets validate a draft bill which bill date is 09/19/2018.

Now Open a draft bill and Click on Validate button.

After clicking on Validate button, Pop up will be open where we can see all bills of ASUSTeK(without current draft bill).
Details of Bills:
1) Vendor Bill : Number of related Bill.
2) Bill Date : Bill Date of related Invoice.
3) Due Date : Due Date of related Bill.
4) Total : Total amount of related Bill.
5) To Pay : Payable amount of related Bill.
6) Currency : Currency name of related Bill.
7) Status : Status of related Bill.
8) Vendor Reference : Vendor Reference of related Bill.
9) Source Document : Source Document of related bill if Bill created from Pruchase Order.

By Clicking on Validate button from Pop up screen(Wizard), current draft Bill will be Validated and Its status will be change to "Open".

When Accountant validate a draft bill and not found previous bill of related Vendor, Below messagae will be show in Pop Up screen and simply Accountant can validate from pop up screen.