Hello @JibbyFlow!
Giving a class to element is not always necessary, but there is some situations when classes will make site more stable and clear. Also, you don't have to give new class to every single element, class mean just some certain style. So you can create 1 class and apply it on different elements, just for give them same style.
In your situation with links, they really has no stable width and height. Yet text inside the links is changing it's size on hover, that automatically change the link "size" (make it bigger or smaller). And it is surely affect other links - it actually moves all the links around.
These links need the width. It will keep all of them on the stable places but I would not recommend to do this without adding class.
Also, I would recommend you to watch this tutorial for understand when and how to use links:
http://tutorials.webflow.com/intro-series/using-links
Regards,
Anna