Retail space should be the right depth i.e. deep enough to accomodate the expected or hoped-for users.
In a discussion on Slog about some proposed neighborhood development in Seattle, one of its most sophisticated commenters criticized a project because its retail spaces were not deep enough. He wrote:
Maybe it goes way back, but if it does it would be highly unusual. And note that the description says 3500 sq ft of retail, and that strip looks 100 feet long, which means an average depth of 35 ft. -- not ten, but nowhere near deep enough to provide adequate retail space. They should go all the way back to the back of the lot.
Assuming that the lot is 100 feet deep (typical minimum) then you'd have retail spaces which are 100 feet deep. Not a good idea for a neighborhood setting.
That's designing yourself into a spot where you MUST have tenant which needs a large space — typically a national or large regional such a Bartells or Wallgreens drugstore — rather than the idiosyncratic "mom-and-pops" which make a neighborhood streetfront diverse and engaging. A typical space for a small store is 1000 SF, (though it could even be smaller.) If the rule is to build retail full-depth of the property, that would mean a retail space of 100' depth by 10' wide -- which is far too narrow. More traditional, practical and widespread is 50' deep and 20' wide. The back part of a retail space is not valuable except for the larger retailer.
In general you size your retail space for the kind of user you hope or expect to see. If you want a Satples or Office Depot you have to have around 7500 SF (that's for their urban stores) and so the larger depth is fine. If you want small business make the spaces smaller. For a small shoe store 1000 SF is appropriate. And for many small or starting businesses, 4-600 is just fine.