For example, you might have data coming from a laboratory, a questionnaire, and from the medical records. A database makes it easy to properly link the information from all three sources. Another example of where a database is extremely useful is in a multi-center clinical trial. The database offers a standard way for data entry that helps avoid the inconsistencies that can plague such studies. Of course, if you have a data set so complex as to take information from three different sources, then you should definitely consult an expert early in the design of your study.
Databases are nice, but they are no substitute for careful planning.
Third, a database is more effective at handling very large data sets . Unlike a spreadsheet, the entire data set does not have to fit into computer memory. If your data set is smaller than this then fitting all of the data into computer memory is unlikely to be a problem. On the other hand, spreadsheets can be up and ready for data entry faster than databases . The extra time required by a database might be beneficial, but for a simple data entry situation, it might just as easily be overkill.