No scope for economies of Scale, this is because there are many small firms producing relatively small amounts. Industries with high fixed costs would be particularly unsuitable to perfect competition. This is one reason why p.c. is unlikely in the real world
Undifferentiated products is boring giving little choice to consumers. Differentiated products are very important in industries such as clothing and cars
Lack of supernormal profit may make investment in R&D unlikely this would be important in an industry such as pharmaceuticals which require significant investment
With perfect knowledge there is no incentive to develop new technology because it would be shared with other companied
If there are externalities in production or consumption there is likely to be market failure without govt intervention
Competitive Markets