There's just one real effect: You get nervous.
Apart from that, you need to understand that helicopters have different operating patterns and requirements. I'm not a helicopter pilot, but I know that although they can hover, they prefer not to do so. At least, not a few hundred feet of the ground. If their engine stops, they need altitude to first set up an autorotation, and then use the rotor energy to cushion their landing. So hovering a few feet above the ground is ok, and hovering maybe 500+ feet is also OK, but anything in between can be a problem. Furthermore, they can fly their circuit differently, and don't necessarily have to aim for the runway. It's perfectly OK for them to aim their final approach to a parallel grass area, and from there hover-taxi to the ramp. So they might just turn to base and final inside of you, and "land" parallel to you. And, of course, they produce quite a bit of wind when hover-taxiing, so you might want to hold on to the controls if they're doing it near you.
If you operate from a field that is also frequently served by helicopters, why not invite one of them over for a coffee and voice your concerns/ignorance. They'll be able to give you a lot of advice.