A large back bar looks like abundance and is largely a display. Most of the money passes through a small number of bottles, and the rest are there for reasons that have little to do with volume.
Sales concentrate in a handful of bottles
A small proportion of the range typically accounts for most of the pours, and those bottles live in the speed rail rather than on the shelf.
The back bar behind them carries the long tail: bottles ordered occasionally, sometimes only a few times a month.
Those slow movers tie up capital indefinitely, since the money spent on them is not recovered until the bottle empties.
Range is a signal to the customer
A visibly deep selection tells a customer that the bar takes drinks seriously, and that impression is formed before anything is ordered.
It also underwrites confidence in the bartender's recommendations, since a customer is more willing to accept a suggestion from a bar that visibly has options.
This is a marketing function performed by inventory, and it is paid for out of the margin on the fast-moving bottles.
Open bottles have a shelf life
High-strength spirits keep almost indefinitely, but anything lower in alcohol does not.
Vermouth, sherry, amari and low-strength aperitifs oxidise once opened, and a bottle poured twice a month is stale long before it is empty.
Serious bars refrigerate these, buy them in the smallest available format, and treat them as a perishable rather than as stock.
Supplier arrangements shape what appears
Distributors often price by volume commitment, so a bar's range partly reflects which suppliers it buys from rather than what it would choose freely.
Listing support, staff training and glassware are all attached to particular products, and those attachments influence what is stocked and what is promoted.
A customer reading a back bar as pure curation is reading a mixture of curation and commercial arrangement.
Menus are the tool for moving the tail
A slow bottle stops being dead capital the moment it appears in a cocktail on the printed list.
This is why house menus so often include one ingredient that seems unusual for the style of the bar: it is being turned over deliberately.
Rotating the menu is therefore an inventory operation as much as a creative one, and bars that never rotate accumulate bottles that will never be finished.