As someone that's worked in the medical field for the past decade, I have often used the '+' and '/' to quickly scribble out an order or notate what happened for the patient.

And @bi4smooth is correct in how to write the '+' and '/', so it is quicker, especially when you're trying to scribble out a note/order as fast as possible and get to the next patient.

@bi4smooth Thanks for the explanation.I genuinely believe that people use it because it's trendy, not because it's easier

Well, not to "pop your bubble" on this one, but when I mentioned it's use by my mother - it was 40+ years ago, and it was while being written longhand, not on a keyboard (much less a phone or tablet!) - so while it may be a "trendy" item today, if so it's a re-trend (or a borrowed trend?)

Truth be told, the "w/" was not written as unique, separate characters, it was all one stroke (I've looked online for an image, but haven't found one)... imagine writing a "w", but taking the upper-right of the w, moving the pen up and to the right very slightly, then striking a hard downward slash...

Similarly, something close to a "+" was used for "and" : imagine a plus character, with the "south" corner connected (by a curve) to the "west" corner... or, start with your pen at North, strike down, straight, to South, curve up and to the left to West, then strike straight to the right to East...

Also, w/f meant "wherefore" (a common legal tern), b/c = "because", b/f = "before", w/h = "withheld", w/f = "wherefore" (another common legal term)... and there were MANY others....

A favorite was "fu" -- which meant follow-up!

I was in my teens, and this is all from memory... there HAS to be an Internet resource for these - but I couldn't find one! My mother is a smart lady, but she didn't "invent" this shorthand! (And I don't mean the "secretarial shorthand" that is a whole other "language"!)

@bi4smooth Thanks for the explanation.I genuinely believe that people use it because it's trendy, not because it's easier

I'll take your word on this one, because I'm probably the last person to know whether something's trendy or not. Some abbreviations are used by people to save keystrokes, but a "/" character, while accessible on a regular keyboard, usually requires an extra step if people are typing on a phone.

Some years ago it was trendy among some younger people to TyPe LiKe ThIs. I saw this on hookup sites like Adam4Adam and gay.com (no longer in the hookup business). While I found it annoying, it was a flag to me that the guy doing it was below my age threshold of interest.

w/ is just shorthand for with...
it pairs with:
w/o is shorthand for without...

while @raphjd says it comes from food service, I first saw it in law offices (part of legal shorthand)... (not saying he's wrong - just stating where I saw it first)

It's waiter/waitress shorthand.