My certificate says "pilot" not "mechanic," and so I make no official claim to knowing anything at all about the inner workings of my ship. I'd imagine that most helo pilots are naturally curious about mechanical things. It's in our nature. And even if I'm not particularly mechanically gifted, I like to know how things work. But as Rich Lee points out, a helicopter pilot need only have "operational knowlege" to be safe. But would more knowlege make a pilot safER? I think that would be hard to quantify, although it would intellectually seem so. Thus, if it gives you comfort to know how the little gears in the watch are actually made, or how a freewheeling unit is constructed, more power to ya!
I try to not make mechanical decisions. If I have any questions prior to the flight, I defer to the mechanic/engineer. If he says "Go," I assume he is right. Have I ever caught something that an engineer missed on his Daily Inspection? Thankfully, no. During flight, if some problem develops, I simply land. Have done it, will continue to do it. I don't second-guess the machine...don't blithely ignore anomalies. And I don't think having any special mechanical knowlege would make me any "safer" as long as there are "real" engineers around. However, having that knowlege could make me a big pain in the arse.
Here in the U.S., a large number of ex-Army aviators whom I've met considered themselves an expert mechanic on the basis of their serving as "Maintenance/Test Pilot" for their unit. It must have been a rotating assignment, because virtually every ex-Army pilot claims to have had that job. Of the egotistical ones, the fact that they did not have an A&P rating nor any practical mechanical experience did not diminish their inflated self-image one bit.
A classic example of how wrong we can sometimes be occurred early in my flying. I was serving as an SIC on a Sikorsky S-58. Prior to launch one day, the PIC (who had a certain, er..."reputation" among the mechs) waltzed into Maintenance and announced authoritatively that our right main gear tyre pressure was too low. The engineer dutifully went out and pronounced it "A-OK." At the time, I was too naive/dumb to see what was happening. And so the p*ssing contest began, delaying our scheduled departure: PIC demanding that the mechanic increase the tyre pressure; the mechanic staunchly defending it as normal. You can guess the rest, can't you? It was the *left* (opposite) tyre that was at too high a pressure! The PIC didn't catch that, of course. All he knew was that one tyre was lower than the other, so the lower one must've been at fault. The mech used that incident to humiliate him. It hardly had any effect.
Taught me a right good lesson, it did. Sometimes a little knowlege is a dangerous thing.