When all is said and done -- your swashplate will have a bit of a tilt to it -- a bit of right tilt for helis with main rotors that rotate clockwise (looking down on the heli from above, and a bit of left tilt if you have a heli whose rotors spin counter clockwise, again, looking down from above. This is natural because even at hover, your heli will lean a bit to the right (CW rotation), or left (CCW rotation). Your heli has to have this small amount lift to the right or left to counteract the sideways thrust produced by the tail rotor. If you get trimmed for a decent hover on a calm day, that small amount of tilt to the swashplate will be there.
As for adjusting the pitch on only one blade, I would assume this has to do with getting the tracking of the blades correct. Ideally, the tip of each rotor blade should fly in the exact same path of the tip of the other blade. Typically, however, no matter how carefully you set up the initial pitch settings, you'll find that one of the blade tips will track higher than the other (that's why you will see different colored "tracking tape" on the tips of a lot of helis). One is usually light colored, the other dark. You hover the heli at eyeball level, and look at the blades. Then you figure out if the light colored blade or dark colored blade is the one tracking high. Land the heli, then adjust the pitch link of the high blade to bring its pitch down until when you hover, both blades track in the same plane.
If you don't have tracking tape, and your blades are out of track, you simply choose one of the two blades (remembering which of the two it is) and arbitrarily lower its pitch. Hover again, and you've either made the tracking better (you lowered the pitch on the correct blade), or made it worse (lowered the pitch on the blade that was already too low). In either case, shut down the heli, figure out which blade to tweak -- and then fine tune until you get your tracking dead nuts on. With good setup on the bench, you're only going to be one, maybe two turns out of kilter from good tracking.
You'll usually want to bring the pitch on the high blade down when you adjust the tracking, instead of bringing the low blade up. In doing so, you'll be able to get the heli to hover well at a lower pitch than you will by tweaking the low blade up to match the high one. It allows you to keep up the head speed at hover. Then, after everything is set right, if you need more pitch at hover, you simply increase the pitch curve setting, or adjust the hover pitch trim itfyour radio has that feature.
Changing the pitch on one blade will NOT result in tilting the swashplate, it will only cause your tracking to suck, and as such, you'll have a heli that shakes real bad, and flies worse.