B. runAs() does not enforce user permissions or field-level permissions in test classes. This means that when you're testing using the runAs() method, Salesforce does not enforce field-level security or sharing rules, allowing you to test the functionality of your code under different user contexts without being affected by these permissions.

D. runAs() can be used inside of test classes to validate record-level security. Although runAs() does not enforce user or field-level security, it does allow you to set up and test under different user contexts to ensure that your application's record-level access is functioning as expected according to your organization's security model.

E. runAs() counts towards total DML statements issued within the transaction. When using runAs() in a test method, any DML operations performed within the runAs block count towards the governor limits for the test transaction. This is important to consider to avoid hitting governor limits while testing.