People did all kinds of diving for decades before computers came along. So, are they "necessary"? No. Having said that, they make diving safer, extend bottom time, keep a log, etc., etc. They're great to have, so why wouldn't you dive with at least a basic one? Do you still use a Nextel flip phone? In fact, do you use anything from the 80s and 90s for anything other than pure nostalgic reasons? Likely not, because there's a better way to do things now. Technically you don't NEED any new tech, but why wouldn't you take advantage of the fact that we are living at the height of civilization and there are really good inexpensive options available? Either way. happy diving....with or without a computer.