The OP's question is so vague it almost does not warrent an answer.
Everything others have said is all true but there are so many different sanding and finishing processes it is impossible to be sure what answer is appropriate.
In this world of Scrolling there are so many different type projects from flat fretwork to sculptured projects. all requiring different sanding methods and equipment. Then there is associated wood working like making frames which also requires sanding and finishing. And , of course, the project wood being used can dictate the appropriate sanding and finishing process.
Yes hand sanding is often necessary, especially for very final finishing and between applications of finishing materials slike Lacquer and Polyurethane.. However, the use of many different power sanding equipment is also useful and appropriate during the actual wood working process. Hand held random orbital sanders, belt sanders, spindel sanders, disk sanders sanding mops, rotary tool sanding drumbs and more are very common sanders used by most of us.