The two main potential disadvantages of having a computer on carpet are:

Carpet collects dust, mite faeces etc, and sheds fibres (fluff), if this is stirred up by feet passing by, floor vibrations etc, it is more likely to be sucked up by the air intake if it is at floor level. That is, bigger dust bunnies.

If the carpet is long pile, it could block the cooling air intake most systems have under the lower edge of the front panel. Tower cases that are designed for floor placement often have large elevating legs to give adequate clearance for good air circulation.