To check target gravities or mash efficiency you would want the hydrometer calibrated to 1.000 in distilled water at the correct temperature, usually 60°.
To check for final gravity of a beer you only need consistent readings to tell when fermentation is complete. If the hydrometer is really far off it may look like a stuck fermentation or over attenuation. This can cause stress and ruin the brewing experience.
I would prefer the hydrometer to be properly calibrated. If the paper scale in your hydrometer slipped out of position once, it will probably happen again. Keep distilled water handle to check the calibration often.