The science is actually pretty simple. Heavy crashing waves will pull sand off of beaches. Light gentle wave action pushes sand ON beaches.
If you've ever panned for gold, you know that the gentle swirling action of a small amount of water can push sand in the direction of the swirl. Think of that as pushing sand ONTO the beach.
But what happens if the water wave is so large that the pull BACK into the ocean is the driving force? Sand removal, of course! Large crashing waves due to a strong tide, or especially in a strong storm can remove large amounts of sand.
The amount of sand movement can be absolutely incredible. As in FEET of sand moving onto and off of beaches.
The term "sanded in" means that lots of sand has moved onto the beaches (typically, as a result of lots of gentle wave action). You can typically tell a beach that is sanded in, because the sand is soft underfoot at the wet sand mark. That's an obvious give-away. The sand hasn't settled yet, and it still being pushed up.
Cuts are a result of waves or ocean tides (sometimes strong rip tides or simple physics can do it) that pull sand off of the beach in large strips. Some cuts are small, as a result of tidal action that creates a channel or trough on the beach, other "cuts" are nearly beachwide, where the sand has been stripped off in massive quantities resulting in almost a Ledge of sand followed by missing sand (like a small cliff!). The science behind it makes cuts unpredictable in smaller versions, but more predictable behind storms. It's why visual inspection is sometimes necessary. There's so many chaotic forces in the ocean, being able to "predict" a cut is very hard, other than at large events. It's why the old-timer goes, looks, and then makes a call.
These "Cuts" have removed a lot of the top sand, and leave the heavier objects behind. These can be honey holes, and in a matter of yards, a good cut can produce lots of heavy objects, including sinkers and gold... which is what folks are looking for.
Also, some storms can PUSH sand up onto the beaches. Not all wave movement is the same. Sometimes, though, those rolling sands that are pushed up will drag stuff with them that is hecka old.
Which all comes down to this... If you're at a beach and NOT swinging a coil, you're not going to find anything, guaranteed. If you're at a sanded in beach, can you still find stuff? Sure! It's fewer and farther between, and what you do find is likely to be littered with lots of light trash. But you can find fresh drops, or drops that simply haven't moved in the sand much (it does take some vibration/water to make that happen).
But... if you're at a beach, and you find a good cut, you can find quite a bit of awesome stuff in a short area, in a short time. That's what the guy is looking for...
Every time I've been to Israel and detected the beaches, it's been in sanded in conditions. The first time, I still pulled a 67-69AD coin, and a 22K gold bangle. The coin was in 4" of wet sand, the gold bangle near the back wall in dry sand as a fresh drop. The second time I pulled NO heavy objects, but managed $160 in change out of the dry sand. In the wet, I found coins back to the 1960's and 50's... Clearly rolled in at some point. Stuff can be found... no doubt. Remember, too, that sand moves with stuff in it... just not typically the really dense stuff, which drops out quickly.
Cheers,
Skippy
