Lots of good responses but lets look at a situation I have seen frequently and I have frequently seen divers with less than 20 dives on. You are diving 18-25 miles off shore. The boat is anchored into a wreck or ledge. There is a mild top water current and possibly some chop or swells. You are at say 75-80 feet but is could be as much as 95. (I know what PADI says but I am talking reality). If you do an open water ascent you will not be close to the boat and you will be drifting away from an anchored boat with divers in the water. You will be unable to find the wreck/ledge if you go back down much less your buddy. You only do an open water assent if you have an emergency and no body to help you or if your buddy has some sort of medical issue.
Normal procedure is to agree to meet at the anchor if separated with an agreed wait time. But stop and wait a bit before returning. If you go for help you go back to the anchor line and go up that.
Situation on wreck is a bit different than a ledge. With a ledge in decent viz if you are separated because you stopped to look around you know what direction they went. On a wreck it is trickier because they can circle around you.
Having a plan is essential.
In low viz on a ledge or sometimes a wreck if you are not careful with your navigation it is possible to get lost. In that case it is important to have an SMB and know how to shoot it from depth. That way the boat knows where you are and can come get you once the other divers are out of the water. No matter what you want to be at the surface before the air gets low. Running a reel in low viz is a good way to avoid getting lost or nearly lost. Also before heading out, explore the anchor area first so you can recognize it from any direction. If you carry an SMB practice with it.
Normal procedure is to agree to meet at the anchor if separated with an agreed wait time. But stop and wait a bit before returning. If you go for help you go back to the anchor line and go up that.
Situation on wreck is a bit different than a ledge. With a ledge in decent viz if you are separated because you stopped to look around you know what direction they went. On a wreck it is trickier because they can circle around you.
Having a plan is essential.
In low viz on a ledge or sometimes a wreck if you are not careful with your navigation it is possible to get lost. In that case it is important to have an SMB and know how to shoot it from depth. That way the boat knows where you are and can come get you once the other divers are out of the water. No matter what you want to be at the surface before the air gets low. Running a reel in low viz is a good way to avoid getting lost or nearly lost. Also before heading out, explore the anchor area first so you can recognize it from any direction. If you carry an SMB practice with it.