Sometimes you see a lot of files FL<date>.dat in DATA directory /usr/sap/<XXX>/<XXX>/data and they may take up too much space, please refer to the following information about what these are used for and how to delete them.
How are they created?
FL<Date>.dat files are written when you have activated the message flow statistics via transaction SMWMFLOW (menu GOTO -> activate statistics). The files are condensed via a report called RSMWM_BSTAT_COLLECTOR (or using t-code SMWMFLOW-> Message Flow Statistics). The results can be displayed in transaction SMWMFLOW.
How to delete them?
If you do not want to have those statistics, you can delete the files and deactivate the statistics as they only contain non business relevant statistical data.
To prevent a quick growth in the size of these files, you can reduce the retention time in t-code ST03 -> Expert Mode -> Collector and Performance DB -> Performance Database -> Reorganization -> For standard data.
To stop the statistics files to be generated or to delete the files, you can go to t-code SMWMFLOW, choose menu GOTO-> Activate statistics-> middleware message flow statistics. The functionality can be switched off by pressing button "switch on/off". The statistics files can be deleted by pressing button "delete statistic file".