The chain holds the ship is pretty true. The west coast method of anchoring barges uses that philosophy. a tug will slow way down, shorten up, then pay out 3 or four layers of tow wire, in a BIG loop like a question mark, then return to the barge, or more frequently just stay out at the end of the wire. the catenary (or what would be the catenary if stretched out) holds both tug and barge quite well. BUT, the west coast uses two shots of chain as a bridle pennant, in addition to the one shot bridle legs. So there’s a whole lot of chain down there. The only part I never liked about this method is: You are intentionally using your main tow wire in bottom contact. This is sort of like asking for chafe and snagging. Towboat skippers try their whole career to keep the wire OFF the bottom. But as usual the west coast does things a little differently!
The original question about digging in, and how to do it is answered by individual preference. When on a large Unit I have both fair tide and head in dropped anchor. The deciding factor is often how hard the current is running, and or the wind. sometimes I don’t have the sea room to round up head into the wind/current! Either way when the anchor sets well you can both see it from the bow answering to the anchor, and the bow watch can see the chain get taut and not skip. How much scope you use depends on location, depth, bottom characteristics, and the ‘reputation’ of the anchor. Some barge companies use a short (15’ or 20’) piece of chain, and the rest wire. That stinks! There is NOTHING quite as satisfying as having a chain rode. Chain holds better, takes less scope per depth, takes abuse better, and make me sleep better.
Your question about increasing scope is pretty important. Sometimes by ‘veering’ out is enough of a ‘jerk’ to pull the anchor out of the mud by free wheeling then stopping suddenly. The term is ‘Walking the anchor out’. By using the windlass and slowly, evenly letting out more scope is the preferable way to get more scope out when needed in adverse conditions. The earlier comment about paying attention and letting out more scope is tantamount. An ounce of cure is often worth way more than several more pounds of cure (or anchor, rode, chain, etc etc etc.) I don’t see why some people ‘chince’ on a little scope when just a shot more would make it all better?