When it comes to materials, there are endless possibilities and no limitations for your sketchbook. That also includes the material of the sketchbook itself - most people will think of a sketchbook as a literal book of paper, but it can take whatever form you please (e.g. digital, canvas, different types of paper that are specific to different materials, it could even be walls, literally whatever you want.) By definition, all a sketchbook needs to be is "blank pages that will document your visual investigations" (Open College of the Arts, 2021). Whether or not an artist prefers to work digitally or traditionally is up to them - there are pros and cons for both choices - for example, traditional sketchbooks are not relying on a power source, so you can take them anywhere (Archisoup, n.d). You can also use whatever materials you want to create these sketchbooks as well - there really are no limitations, apart from personal ones (such as money/price of materials or just not wanting to come out of your comfort zone with a new media). Take Kellan Jett for example - he uses a variety of different media in his sketchbook, ranging from paint to pen to digital drawings. Adding onto that, there is no set way for you to work in your sketchbook either. You can present things however you like. That can include page layouts, text, media, etc. The whole reason for a sketchbook is to allow you to experiment, so by having no limitations your creativity can really roam free (Dunato, 2013). Like Kenn Yap (aka Chroma Moma on YouTube) said, “sketchbooks are a place to fuck up.” (2022). That being said, loose sketches are a great warmup and can really help put you in the mindset of creating. They can also improve your understanding of whatever you are drawing by forcing you to roughly map out shapes and shadows before you get started on a more detailed drawing - or you can keep it as a sketch, its really up to you.