A service may appear profitable as long as the assistance work remains off the count. Telephone calls, clarifications, and corrections take up time that could be taken elsewhere. Registering it allows you to understand which offers require more support and for what reason.
I would distinguish the assistance provided by requests arising from incomplete information or errors. In the first case time is part of the proposal to the customer. In the second, it signals a possible improvement in delivery or initial explanation. Mixing the two categories prevents you from choosing a relevant intervention.
Imagine a small business installing equipment. Calls on maintenance may decrease with clearer instructions. Requests for a particular use could instead justify an additional service, to be defined without taking for granted the customer's willingness to pay for it.
I propose to link the hours to the type of request and the version of the offer. The review may relate to content, organization, or price. The expected result is a sustainable promise, in which the necessary support is recognizable before taking on new commitments.