I think it depends on personal preferences, goals, and circumstances. The most important criterion for evaluating a paper is its quality and impact, regardless of the number of authors. The scope and complexity of the paper may influence the decision to collaborate. Collaboration and communication skills may affect the process and outcome of the paper. Some fields may value single-author papers more, as they indicate originality, independence, and contribution. Other fields may value multi-author papers more, as they indicate collaboration, interdisciplinarity, and impact. And why some people highlight their single authored publications in their resumes, I quess they want to showcase their originality, independence, and contribution to their field.