I think your manager asks a good question, and the answer you give is going to depend on what you are seeing when you do these reviews. For example, if you are seeing a very high error rate in the charges and are having to make many corrections to the coding, then reviewing all of the chart notes would be important for both compliance and reimbursement purposes. However, if you are finding that most or all of the charges are correct and you are simply 'signing off', then I would also be asking whether or not it is really a good investment of time to be reviewing every one.
Most organizations, especially larger ones, do not want coders reviewing every note because, quite simply, it is a very costly use of resources to pay coders to review things that don't need reviewing. So practices will set up audit programs where samples of notes are reviewed regularly, and when problems are identified, or it is noted that specific providers or clinics have high error rates, then coders focus on those areas that need their attention, both in terms of reviewing coding for accuracy, as well as in conducting education for those clinics and providers so that, whenever possible, those areas may be able to get to a level where they no longer require 100% review of notes. Areas that have higher rates of error, or for which errors may have a high financial impact, should have higher rates of review. Areas where errors are infrequent or have minimal impact can safely be reviewed at a lower frequency.
So I'd recommend discussing this with your manager from this perspective - let your manager know what you're seeing that supports a high rate of reviews, but also consider opportunities where some charts may not need reviews so that your coding skills can be redirected in a way that will help support the practice's financial health going forward. Hope this may help some.