Ski Platform use with engine running?

I have a 1986 ski nautique 2001. I see everywhere it's advised to shut off the engine while swimmers climb aboard. Is this really necessary? Whilst in Neutral and idling the prop doesn't turn. And there's the safety neutral switch you can keep pulled out, and the swimmer probably won't stick his foot in the prop anyway (although that is always a possibility).

Let's say I'm running the boat all day with a youth skiiing group of several dozen skiiers. It'd be pretty had on the engine and starter and battery to turn it off and on dozens of times a day. What are your thoughts? I want to be safe and safety is more important than wear and tear on the boat. But then it seems safe to keep it running does it not?

+1 what he said and I always communicate that the engine is off and wait for the skier to let me know they are clear before starting the engine.

I agree. Shut it down.

Always shut it down between skiers/boarders using the swim step. CO is a silent killer.

Some very good points.. I'm glad I asked. It seems wise to stop the engine. Thanks everyone.

^^^
Engine on when booting up, I'm idling down river at that time anyway. The rider typically steps or hops off the back while I'm underway at clutch speed. i feel this is pretty much SOP for most operators.
Engine OFF when boarding the platform all and every time without exception. Engine OFF and handle in. Those are the rules. Lose a $150 wake-board mainline in your running gear once and you'll add that to the list pretty quick.

63 skier, your note about turning back slower and more carefully hit an old nerve.
We were on our local lake bare footing one night with the owner of west coast Correct Craft. This was 1983. He asked me to sit on the gunnel behind him to offset the guy on the boom. I had one hand on the ski pole, The footer fell off the boom and the owner spun the wheel hard left at barefoot speed, I tried to hold on which was a mistake because it slowed my ejection. I hit the water knowining I was in deep shi* and landing digging hard to get deep fast.   I watched the prop go right over me. Missed by maybe 18 inches.
The guy forgot I was behind him and could have killed me.
Then not knowing if I was alive or not and panicked, he kept spinning circles looking for me till my wife told him to shut it down. Then I came up for air. It was a learning experience with all seasoned boaters in that boat.   

Thanks, that note from 63 Skier brought back that bad memory. If I had just let go in the turn I'm sure the turn would have thrown me well out of the boat path but first response was to hold on which was futile with one hand.
Mark