It s bad even if air doesn t flow into or out of the case here however if your pc sinks into the carpet a bit heat can build up underneath due to the lack of airflow.
Computer on floor bad.
For example cigarette smoke and pet fur will exacerbate those problems and putting your desktop pc on the floor will ensure more of that dust hair and debris will get sucked into the intake.
Not necessarily bad but not the best either.
You ll collect more dust on the floor requiring cleaning more frequently.
I slid a piece of cardboard under there and it was fine.
That s when keeping on the floor can be a bad idea.
On the floor keeping your pc on the floor is widely considered the worst place due to the amount of dust and pet hair that can get inside your tower especially on any type of solid flooring.
If you don t have a choice you ll want to buy some compressed air and regularly blow out inside your computer.
Of course if you have short carpet on your floor the pc may be able to sit on that carpet with plenty of airflow underneath.
If you have bottom intakes then you need to ensure you have enough clearance for air to get to those intakes.