It's generally better to have a second set of eyes in the cockpit to look for traffic during VFR flight. But a two-pilot crew in a single-pilot helicopter is not *always* safer, nor is it *always* less workload for the PIC.
As long as both pilots are equally rated and there is a clear definition of who is PIC then yeah, go for it if you want. But there are other cases when it's not beneficial.
My boss used to charter (or "borrow") single-pilot fixed-wing aircraft for which I was not rated. He would insist that I go along on these flights "...as copilot" because while he was happy to fly in his single-engine helicopter with just me, he would not fly in a fixed-wing without two (turbine) engines and two pilots. So I'd go along and pretend to be a copilot. I've flown as "copilot" in Piper Cheyennes and multiple Beechcraft 200's (and even a 350), and various Cessna Citations. All of the PIC's were people I'd never flown with before.
Lots of times the PIC would ask me if I wanted to do something...handle the radios or whatever. I usually said, "Nope! I'm just going to sit here and look for traffic." When you take a guy who's been flying primarily as a single-pilot and then give him an unfamiliar copilot, you are *not* enhancing safety. Because now the PIC has to monitor everything that the "SIC" does to make sure he did it right. It actually increases his workload - which does not increase safety. It actually has the opposite effect.
I've flown as PIC with other similarly-rated pilots in small aircraft. They usually always want to participate in flying the aircraft - take away some of *my* duties as PIC. I usually deny the request. I say, "When you're flying, *YOU* do it all. When I'm flying, *I'LL* do it all." And then I'll let them do as much of the flying as they want. It's not that I'm a tw@t. Nobody needs a copilot in a small, single-pilot aircraft. Hey, you want to sit there and look for traffic, fine. But don't expect me to sit here with you "handling the radios" while you miss a call from ATC because you're gabbing away trying to impress me with how much flight time you have.
Yes, that's happened more than once. I say, "Uhhh, I think that was for us." They didn't catch the call because they're usually not familiar enough with the N-number to hear it over their own voice. So much for reducing my workload by letting someone else handle the radios, eh?
Throwing a "lone-wolf" single-pilot into a two-crew situation can be a recipe for disaster. I would advise pilots to be very, very cautious about who they let become a "copilot."