Application allow listing is the most effective technique to prevent bloatware, unauthorized software, or unnecessary applications from running on devices. Allow lists work by permitting only pre-approved, trusted applications to execute, blocking everything else by default. This is a recommended best practice in Security+ SY0-701 for reducing attack surface, preventing malware, and maintaining lean, hardened system images.

Bloatware often comes pre-installed on devices or is unintentionally installed by users. An allow list ensures only authorized applications required for business functions can run, thereby eliminating bloatware risks.

Disabling ports/protocols (A) hardens network access but does not prevent software installation. Default password changes (C) improve authentication security but are unrelated to software control. Access control permissions (D) restrict who can access what but do not prevent installation of unnecessary apps.

Thus, the correct answer is B: Application allow list.