If these errors are exposed at the web pages somehow i.e. "Exception" or "Error" word is present you can consider adding a Response Assertion to check that the page does NOT contain "Exception" word. Similarly you can use assertions to check that response matches your expectations.
However according to JMeter Performance and Tuning Tips guide, assertions have cost so use them with caution.
If there is no explicit affect you need to determine implicit impact, i.e. increased response time, timeouts, missing results, etc.