Function follows form usually end up with great outer design and satisfying appearance from outside view but the we don't know what happens inside. For an example, the picture below shows the MIT Strata Center building by architect Frank Gehry. The outer appearance of the building is magnification and unique however the building blocks the emergency exit of the building. Therefore, this building is much for the design and when it comes for the practicality it is considered as a bad design.
Example of function follows form: MIT Strata Center
On the other hand, form follows function is designed according to its purpose, thus fulfilling the function of the building or an object. For an example, the picture below shows an image of a designer's sofa. This sofa is designed for people to sit on it. Therefore, it follows the basic structure of a sofa but however it is designed in a creative way without neglecting the function of it.
Form follows function: the sofa is designed based on its function.
A glass tube act as a bird cage. It has a hole for the bird to breathe. This is an example of form follows function because it does not neglect the function as a bird cage.
Therefore, in design there is no one way of doing thing. Every designers has their own way of doing this. As long as it function able and practical any way is correct in achieving a good design. Form follows function or function follows form are both acceptable in design.