Setting this property to true allows users to resize forms, click buttons, etc. while reports are being generated in synchronious mode. This makes applications more responsive, and is necessary if you want to provide a "Cancel Report" button (otherwise users wouldn't be able to click the button until the report was done).

Setting this property to false will cause reports to render slightly faster.

The code below implements "Render" and a "Cancel" buttons attached to a FlexReport component.

The "Render" button checks whether the FlexReport component is busy before starting to render a report. This is necessary because the user could click the "Render" button several times in a row, before the component got a chance to finish rendering the report. (Calling the Render method while the component is busy throws an System.Exception).

The "Cancel" button checks whether the component is rendering a report and sets the Cancel property to true.

_c1r.DoEvents = true;
            
private void Render_Click(object sender, EventArgs e)
{
   if (_c1r.IsBusy)
   {
       Console.WriteLine("Cannot render now, component is busy");
   } 
   else 
   {
       ppv.Document = c1r;
   } 
}
private void Cancel_Click(object sender, EventArgs e) 
{
   if (_c1r.IsBusy) 
   {
       _c1r.Cancel = true;
   } 
   else 
   {
       Console.WriteLine("No report to cancel");
   }
}

Reference

FlexReport Class
FlexReport Members