Before purchasing Wire cut cnc edm I just wants to know about disadvantages of it over using mechanical lathe machine.
Wire EDM and a lathe aren't really directly comparable. Wire EDM is typically used for profile cutting of very hard materials such as hardened tool steel with good dimensional accuracy and may also be useful for producing very small holes or slots.
As a result it tends to be quite a specialist process and compared to conventional machining processes on materials with good machinability it will tend to have a low rate of material removal and may be less versatile.
I'm tempted to suggest that if you don't already know why you need an EDM machine you probably don't need one.