I strongly disagree that one should always dive with a buddy. But I’ll also say that one shouldn’t dive alone. Exit and entry are usually the most dangerous part of the dive.

Diving in low vis, spear fishing, or confined spaces don’t match with having a dive buddy. But they do match with redundant air supplies and other safety measures I mention in another comment.

Also unless your buddy is literally within arms reach at all times, they are not a redundant air source.