Yes it is if you want your source reconstruction to be as accurate as possible. Important is to realise that there are different types of errors: You can have random errors in each electrode location. Assuming that you use a non-linear dipole fit method for source localization, you will get an increase in your residual variance. The fitted source location does not have to be wrong. You can also have a systematic misalignment of all your electrodes with respect to the volume conduction model of the head. That will result in a systematic mislocalization of your sources. So the latter error should be a bigger concern to you than the first error.

See also

• Wang Y, Gotman J. The influence of electrode location errors on EEG dipole source localization with a realistic head model. Clin Neurophysiol. 2001 Sep;112(9):1777-80.
• Khosla D, Don M, Kwong B. Spatial mislocalization of EEG electrodes – effects on accuracy of dipole estimation. Clin Neurophysiol. 1999 Feb;110(2):261-71.