So what happens if the current picks up, changes direction, a mask gets knocked off, or any of a number of other things that can cause your SAC rate to increase? You've only got 700 psi, your buddy is blowing through his gas and you're stuck at 100ft for some reason. Guess who's making it to the surface? My bet is neither of you. That is why gas planning, even at the basic open water level, is not only important, but necessary. If I'm doing a 100ft dive and I'm on a single HP100 (equivalent to a standard size single tank in the UK), we are starting the ascent at 1500 psi. That is minimum gas. Why? Because if my buddy has an issue, I know we can both make back to the boat safely, complete with stops.
I think I'm being misunderstood. It's coming down to semantics again.
What you are describing above is what I called a dive plan. You are providing an example with a specific depth where I was providing a general case without a depth. If you are still having trouble with my example plan then substitute the required depth for ascent or keep the 700 and let's set the depth to say 25 feet. I agree with you that at 100 ft you need to ascend with more than 700.
Going back I made these specific definitions:
Gas planning: used to make a specific time or goal oriented dives where specific SAC/SRV rates are needed to determine tank size to accomplish the goal. The goal in this case excludes trivial exploring.
Dive plan: a dive that doesn't require gas planning.
I call your example above a dive plan because you have no minimum time or goal like bringing up an object therefore SAC/SRV aren't required. We watch our SPG's and agree to ascend when one of us reaches whatever minimum psi we set. Notice I didn't say we shouldn't take into account our buddies breathing rate (SAC) but that a specific SAC number and hence we need this tank (gas planning) are not required.
Now, let's beat that dead horse:
Dive 1: wreck penetration to explore a room midway into the ship. This is a specific goal that requires a minimum amount of time to accomplish and therefore we need (REQUIRE) gas planning.
Dive 2: same as above but the is not required. If we make it fine. If we don't fine. Our dive plan calls for turning our dive at 2000 (assume an 80 and rule of thirds). We're not going to calculate SAC/SRV so we don't even know if an 80 is enough air. There is no gas planning. On this dive we only make it a 1/3 of the way in when we reach 2000. So we turn the dive. All we did is dive the plan and watch our SPG's.
Let's also beat the dead horses brother:
What all of you are doing is conflating my definitions of dive planning and gas planning into one lumpy definition and confusing what's needed with what's nice to know and then providing exceptions to disprove my argument. What does a PADI AOW or a vaction diver REQUIRE to make any dive within rec limits: watch your SPG and apply common sense and your basic training. No gas planning needed (as I've defined it). Thousands of divers are doing just that.