Eddy
No. Flexwhere can be used without Flexwhere for Desktop. (formerly TrayApp). Flexwhere for Desktop does make it much easier for employee and more accurate for statistics.
Without the TrayApp, employees must book a place via their smartphone. That is the only indication that the workspot is busy. This requires discipline from your employees when making bookings and canceling them if necessary.
Even with the TrayApp, employees still book a workspot via the mobile application.
With fixed PCs and docking stations, the TrayApp automatically registers who logs in and when. An employee with a laptop without a docking station clicks on the occupied workspot via the TrayApp on the floor plan.
To know for sure if a workstation is occupied and by whom, Flexwhere for Desktop is the best option.