PowerServer Performance Tuning Guide
Technique #2: thin-out “heavy” UI logic

The DataWindow RowsFocusChanging and RowsFocusChanged events can be triggered under many situations, especially when a DataWindow retrieves data. Since data is usually automatically retrieved into DataWindows when a Window is opened, if a lot of code is written into the RowsFocusChanging and RowsFocusChanged events, it will significantly prolong the time it takes to open the Window and display the DataWindow. PowerServer recommends that you do not write code into RowsFocusChanging and RowsFocusChanged events unless it is necessary.