What are the disadvantages of preventive maintenance?

The disadvantages in preventive maintenance are the routine job of Cleaning of messed up equipment from the accumulation of dirty dust, Oil clogged ,carbon accumulations on the surfaces which eventually it take time to finish.

you can not manage properly maintain a distance

there is no advantage of doing PPM , PPM is an important part of project SLA , however you can use the reliability engineering to minimize your needs for implementing PPM and accordingly minimize your costs and keep the same level of service

There is no any disadvantage from the PPM but some companies are thinking PPM will cost them extra but not taking proper PPM will reduce the corrective expanses