At the lab where I used to work, we had both prospective clinical study which is collecting data in real time or retrospective which is using old data to be analyzed. The way the studies were organized were so that the previous study can build the groundwork for the next study either as pilot data for a new grant or just a side dataset contributing to the next project. Doing it this way is more efficient in terms of time. In many cases, more data is always better than less data because we can (most of the time) analyze it in the future which could be helpful in a grant writing or writing a journal paper.