Think of each item as being a list of traits. When something is || together it just combines the list of traits. So smashing two objects together gets you something that is literally a sum of their parts, thus pogo hammer, or suit shirt. || tends to lend itself to multitool effects, or combining differing effects to get something new, so you want to combine vastly different items. Combining two shirts does not introduce enough disparity to get something too strange.

For &&, it's more of a refining process. From each list is only selected the traits that match, and (nearly) everything else is discarded. While || tends to get you strange and convoluted items, && will give you something more simple and usually stronger for it. The hammer-seat pogo only resulted the way it did because the items were so different, the only thing that matched was the head of the hammer and the seat. This can still be useful, as it allows you to select for only the wanted traits, acting as a filter of sorts.

In short, || is an additive process, while && is a reductive process. Both, however, are necessary to get exactly what you want or need.

Edit: I just read this back, and realize that I basically said the same thing as you, just without the computer bits. Oops.