Sally Lesser really needs a bigger apartment. Instead, she has a storage unit.

Into her 70-square-foot nook goes everything she cannot cram into the one-bedroom apartment in Brooklyn Heights she shares with her husband: out-of-season clothing, old files and Christmas ornaments, playbills from long-ago shows, even their grown son’s childhood toys. All for $275 a month.

“We could not live without our storage unit,” said Ms. Lesser, 66, a costume designer. “Where are those Thomas the Tank Engines going to go?”

For many New Yorkers, a storage unit or two (or three) is the only solution to living small. It is the spare closet or extra room that they don’t have, or can’t otherwise afford in a crowded city with ever shrinking and more expensive living quarters, including so-called micro-apartments that are barely larger than storage units themselves. It is a temporary holding place for those in between jobs, moves, marriages and divorces, and an extension of the workplace for small businesses.

But as self-storage buildings have multiplied across the city, they are drawing increased scrutiny from city officials and community groups who say they take up space that could be used for something more productive. Now the city is proposing to restrict the development of new self-storage buildings in some industrial areas in the boroughs outside Manhattan, as part of a broader strategy to save more land for manufacturing and industry.