1. The advaages of sketching wireframes is that they're speedy, flexible, and you can focus more on the structure than the visual design. The problems with sketching wireframes, however, is that you can't undo any mistakes that you make and you don't have any templates or elements to reuse. There's also the fact that it's also low fidelity and non-interative as well.
If I were to pick a wifreframing style, it would be sketching because it helps me to craft a blueprint for the design I'm working in before I think it's ready to put into action. Skeithcign it also a great way to help grow your skills when you're trying various different ideas and techniques.