By navigating to Settings > Advanced > Workflow, you have the option to toggle 1-click approval with a single click:

...then your coworkers will always have to confirm that they want to approve the expense. In other words, one extra click whenever they click Approve on a document:

...then your coworkers will be able to approve expense without the extra confirmation of approval. In other words, the document will be approved as soon as the coworker clicks the Approve button once.