Variables that are declared static stays in the memory till the program executes thus taking extra space.
The use of static may be beneficial if you want to use/retain a value for a long period of time, however declaring all variables as static is not recommended and is not a good practice . If you make a habit of declaring all value as static your program will eat unnecessary memory.
Other than that static variable doesn't comply with OOPS concept where scopes, abstraction and encapsulation are defined along with the effervescence object. Through which you can call and delete variables at will.
The biggest disadvantage of using static variables will appear if you are working in limited memory space (such as mobile applications) in that case you application will crash if it is overhogged by variables and less memory space.
If you want to store a value permanently there are other ways around like database, files etc makes the job easier and cleaner.
Just my 2 cents.
