Using Energyplus 8.9 and
Output:Diagnostics,
DisplayUnusedSchedules

for linked idf file, the schedules
AIR VELOCITY SCHEDULE
CLOTHING SCHEDULE
WORK EFFICIENCY SCHEDULE

are listed as unused, but they are referenced by the People object.
People,
Warehouse Office People, !- Name
Warehouse Office, !- Zone or ZoneList Name
Warehouse BLDG_OCC_SCH, !- Number of People Schedule Name
People/Area, !- Number of People Calculation Method
, !- Number of People
0.0210972644167511, !- People per Zone Floor Area {person/m2}
, !- Zone Floor Area per Person {m2/person}
0.3, !- Fraction Radiant
, !- Sensible Heat Fraction
Warehouse Office Activity Schedule, !- Activity Level Schedule Name
, !- Carbon Dioxide Generation Rate {m3/s-W}
, !- Enable ASHRAE 55 Comfort Warnings
, !- Mean Radiant Temperature Calculation Type
, !- Surface Name/Angle Factor List Name
Work Efficiency Schedule,!- Work Efficiency Schedule Name
, !- Clothing Insulation Calculation Method
, !- Clothing Insulation Calculation Method Schedule Name
Clothing Schedule, !- Clothing Insulation Schedule Name
Air Velocity Schedule; !- Air Velocity Schedule Name

And deleting those three schedules from the idf file results in a severe error.



idf file google drive link
https://drive.google.com/file/d/14ofP...

err file google drive link
https://drive.google.com/file/d/1tAXU...