Neat handwriting is considered to be a reflection of someone's good organizational skills. However, writing something clean and free of mistakes takes a lot of practice and attention to detail. The worst enemy of neat & organized handwriting is scribbling lines over mistakes. Whether it is a research paper or anything else, scribbled lines over mistakes make it unprofessional and untidy. The solution is to write random letters over the word to hide the mistake.
A bunch of letters can hide embarrassing words that could make the written work unprofessional. In addition, it will help make the words completely illegible for the reader.