Figure 1: People with Intellectual and Developmental Disabilities (IDD) use personal data to make sense of everyday life. Participants with IDD most frequently used data to track activities of daily living (e.g., nutrition log, checklist, and everyday documentation); however, this data was often invisible to people despite being used in a variety of common scenarios, such as to advocate and shape treatment in healthcare applications. We synthesize limitations in existing approaches to working with data and opportunities for using visualization to enhance data accessibility for people with IDD. For example, participants and their caregivers identified a range of scenarios where data had significant potential to help people with cognitive and communicative impairments better participate in social and self-advocacy situations.