Ok to adjust balance to achieve center vocal image?

I have an all analog tube vinyl system and don’t remember having to adjust my balance setting in order to achieve a center vocal image. I do now though. I’m getting a left leaning vocal image with the balance set to zero. Is there a good way to see if this can be fixed so I don’t need to balance adjust to achieve a center vocal image? Could it be a preamp tube going out? Something else? Any harm in just continuing to adjust the balance - meaning am I experiencing any signal loss doing so? 
Thanks! Paul
One common mistake with speaker setup is the assumption that everything should be set up symmetrically -- as judged by the eye. But what if there's a wall beside one speaker and a bookshelf beside another? Or a hallway at one reflection point and a window near the other? That will un-balance the sound. The solution is either with treatments or, more simply, to understand the acoustics happening and adjust the speakers so that they match *aurally.* Maybe that's not your issue, but it seemed worth mentioning.
For such a simple tonearm, the Concept/Verify magnetic tonearm can be a bit tricky!

Its vertical tracking force can vary wildly with vertical motion, increasing in pressure/force as the arm is raised. This is why Clearaudio supplied a super low-profile balance beam to be placed directly on the platter when setting VTF.

Any VTF reading taken above the record playing surface will be artificially high. When cueing the tonearm manually by hand, you may be able to notice the weight of the tonearm feels heavier as it's lifted. Also, optimally set up and playing, this tonearm tube really begs to be parallel to the record in order for its flat supporting magnets to be parallel to each other at the fulcrum.

After the turntable is leveled, Anti-Skating is a simple adjustment underneath the tonearm mount consisting of twisting the knob which is the anchor of the tonearm's supporting braided-wire. Typically these are best left at their factory position, usually marked with a black sharpie line and optimized for 2~2.5 gram tracking weights. When viewing the adjustment knob from underneath the tonearm, clockwise increases Anti-Skate, placing more pressure on the right channel outer groove wall & counter-clockwise would be vice versa.

Hello paulgardner,

     An imbalance could come from numerous sources, it may be best to use a process of elimination to narrow down the root cause of the problem.  Here's some suggestions:

1. speaker cables- with the amp off, swap the left speaker cable with the right speaker cable. Turn the amp back on, set the balance control to the center position and try it out.
      If the center image pulls to the opposite side, it's your amp.  If it still pulls to the same side, suspect the speakers, the cables/wire or your room.  You can verify your speaker cables are fully functional with a continuity check using a multimeter yourself or just bring them to an electrical repair shop and have them verify they're good for you.

2. speakers- with the amp off, switch your left and right speakers and connect them with speaker cables you've verified as fully functional. Turn the amp back on, set the balance to center and try it out again.
     If the center image moves to the other side, it's your speakers. 

Best wishes,
Yes indeed. Trouble shooting could begin on either end of your system.

On the front end, see what happens when you swap right & left phono inputs. You may or may not find the answer there . . .
As Tim described, you can do switching starting at either the front end and working down the line, or the other way (from speaker back to source).  This will allow you to isolate the source of the problem (assuming it is in the component stream and not the room or your own ears).  This switching also involves moving tubes from one side to the other to determine if the weakness is in one pair of tubes.

Right now, I have a substantial imbalance that I've isolated to my linestage, and it is not the tubes.  Because I don't have any other obvious problem with the sound, I have been utilizing the balance control to compensate.  At some point I will bother to have this looked into by someone more competent than myself.

I think balance control is an essential feature.  There is always some some imbalance, particularly with phono cartridges.  It is amazing how small an imbalance is actually audible.  When I had a Levinson No. 32 linestage in my system, I could change volume and balance by as small an increment as .1 db.  While a whole db of volume change when playing music is not reliably audible, a change of as little as .2 db in channel balance IS audible.  That is why I had the builder of my tube linestage include balance control (I also insisted on remote volume control, something he was not normally inclined to include in his designs).