User needs understanding is critical for developing useful and usable clinical research decision support. Existing methods largely depend on self-reporting and often fail to elicit implicit or fine-grained user needs. We hypothesized that functional software would address this problem by presenting to users existing technology while simultaneously encouraging users to optimize workflow. Using clinical research visit scheduling as an example, we used a piece of software under development that was called IMPACT to reveal user needs iteratively. The identified user needs explained why most clinical research coordinators still rely on paper to schedule clinical research visits. The common user needs themes such as information completeness for software to be useful may generalize to other clinical decision support. This paper contributes valuable firsthand knowledge about user needs for decision support for clinical research visit scheduling among clinical research coordinators and a generalizable methodology for collecting and analyzing software usage data to inform user needs elicitation.