welcome aboard nurseterri2. When you say "loose sand", I presume you mean the "dry" sand? (as opposed to the "wet" and in the inner-tidal zone, eh?). And do you mean lakes or ocean beaches? There is no one "answer" for your question. On ocean beaches, sometimes the wet sand is better. Particularly if erosion has been occurring where mother nature leaves scores of targets nicely grouped for you to harvest

Other times the wet sand is totally devoid of targets, if the sand movement is "coming in" and the wet sand is "soft". In those cases, the stuff will have gone too deep out of range, and you won't even get a signal. In those cases, you're better off in the dry sand, where at least you might get a beep
And when you say "backyards", that too is a nebulous question. I mean, "backyards of what home?" Obviously some might be good, while others can be nothing but a wasteland of junk. Obviously they're going to vary, home to home, depending on who lived there, how inclined they were to fumble-fingers loose stuff, how old the house is, how junky that yard is, whether or not its been hunted before, and a million other factors.