Modern web applications use features like camera and geolocation for personalized experiences, requiring user permission via browser prompts.To explain these requests, applications provide rationales-contextual information on why permissions are needed.Despite their importance, little is known about how often rationales appear on the web or their influence on user decisions.This paper presents the first large-scale study of how the web ecosystem handles permission rationales, covering three areas: (i) identifying webpages that use permissions, (ii) detecting and classifying permission rationales, and (iii) analyzing their attributes to understand their impact on user decisions.We examined over 770K webpages from Chrome telemetry, finding 3.6K unique rationale texts and 749 rationale UIs across 85K pages.We extracted key rationale attributes and assessed their effect on user behavior by cross-referencing them with Chrome telemetry data.Our findings reveal nine key insights, providing the first evidence of how different rationales affect user decisions.