If your turntable platter is not perfectly level it will affect the way the stylus sits in the groove, causing channel imbalance and possibly uneven wear to both the record and the stylus.
Ensuring that your turntable is perfectly level is necessary for gaining maximum performance... and that goes for the rest of your equipment too! If your turntable isn't level then it will have an effect on all other parameters such as tracking, Anti skating/Bias and cartridge alignment
Size 30mm diameter x 9mm high
Turntable Bubble Level
Suspended turntables are designed so their suspensions work in the vertical plane to give "pistonic" motion usually tuned well below audio frequency. If the table is out of true the "pistonic" motion picks up all sorts of parasitic motions, wobbling all over the place sometimes in the audible range (>20hz) and at the frequency of record warps. This is why quality suspended tables take so long to set up - to get the bounce spot on - if the turntable isn't level the bounce will NEVER be right.
One of the critical components for a turntable is the main bearing which must offer minimal friction and hold the platter fixed in all planes except rotation - all this with minimal play and as little vibration as possible. All such bearings are designed to work with the turntable level with all forces acting vertically downwards. Tilt the table and you add a horizontal force which will compromise performance and over the long term cause the bearing to wear unevenly, non-suspended turnables often have very heavy platters which exacerbates the problem