A deeper base cabinet offers increased storage but you often find yourself too far away from the mirror to conveniently apply make-up or shave. Two alternatives to counter balance deep base cabinet designs : either use a top mirror cabinet so get the mirrored area closer to the face, or go for a structured/ curved vanity top where the depth of plan is reduced in some area(s).
Read this carefully, especially if you have a nearsightedness condition (myopia).