Developing robots that are useful to older adults is more than simply creating robots that complete household tasks. Careful consideration of the users' capabilities, robot autonomy, and task is needed. Perceived usefulness, according to the Technology Acceptance Model (TAM), is described as a person's perception of how well the technology's capability matches his or her own needs. The purpose of this qualitative study was to investigate the construct of perceived usefulness within the context of robot assistance and user capability. Two user groups participated: mobile older adults (N = 12; used no ambulation aid) and older adults with mobility loss (N=12; used walker or wheelchair). Participants took part in a think aloud task. We asked participants to discuss their robot control preferences for household tasks (e.g., clean, find and fetch). Older adults with mobility loss tended to prefer to command/control the robot themselves (low robot autonomy); however, mobile older adults' preferences were split between commanding/controlling the robot themselves (low robot autonomy) or the robot commands/controls itself (high robot autonomy). Reasons for their preferences were task specific and related to barriers/facilitators of robot acceptance, such as trust, reliability, and user need. Findings provide practical guidance to choosing robot autonomy level, broadly defined, for different groups of older adults.