This is really complex and tough. If it's done quantitatively -- say, no more that one Duane Reade in a half mile radius -- that doesn't prevent a Duane Reade from opening where the locals really don't want it, and may prevent one where the locals do want it. If it's done by local preference, well, the community board is inviting a fight between locals with differing preferences, or making determinations on it's own caprice, which invites law suits from the rejected applicants.
But a special zoning, which is what the CB is considering, seems to me to be worse. If it defines the number of chain stores in particular areas it will freeze those areas based on current circumstances. In five years that plan will be obsolete. Few documents are as depressing as old urban plans.