By Amy Westervelt Small companies are finding new ways to make co-working pay off.The practice of sharing office space with other businesses has boomed in recent years—mostly as startups look to cut down on overhead and get a chance to brainstorm with their peers.But as the concept of co-working gains traction, small firms are starting to put new spins on it. They're finding ways to use existing co-working setups to cut costs and boost efficiency, and they're coming up with ways to put the idea into practice for themselves—without a third-party space.In one setup, a business keeps a home office but uses co-working spaces to let employees work remotely. Sometimes this arrangement is a perk for employees who have a tough commute, other times it's a way to save on expenses when moving into new territory.Dark Arts Consulting, an IT consulting firm based in New York, has used its membership with co-working office provider Regus to expand into territories in New Jersey and Pennsylvania. Lee Solt, Dark Arts Consulting's founder and president, says that expansion would be a logistical nightmare without the option of co-working.Now, though, "I can go out and hire the salespeople and engineers I need without the added expense of an underutilized office," he says.Still, the usual problems of telecommuting apply. For instance, not having a permanent office could make remote employees feel disconnected from the company and make it more difficult for their managers to oversee their work or provide support.Another variation on co-working is an arrangement where businesses with more space than they can use rent out their excess room to another company. When Yoav Lurie, co-founder of utility consulting firm Simple Energy, went looking for office space, he knew he wanted to be in downtown Boulder, Colo., and he wanted room for his company to grow. But Simple Energy couldn't afford its dream office. "Even if we could have afforded the space we wanted, we wouldn't want to burn $10,000 a month to save space for later," he says.Then a brokerage service, PivotDesk, connected him with small-business owners who were looking for affordable office space. Mr. Lurie took the dream space and rented out 18 extra desks at $350 each per month, allowing him to offset half his rent. He also wound up hiring staff and landing a new board member from the tenants that he found through PivotDesk.Compatibility can be an issue. Host companies have complete control over who can see and rent their space, and under what terms—but that level of oversight doesn't eliminate the chance that they'll end up with an unsuitable tenant. Companies could also need their excess space quickly and thus need to move tenants out quicker than expected, but PivotDesk says it manages any such scenarios to ensure both the host company's and the tenant's satisfaction.In other cases, co-working companies are trying to ensure a good relationship—by doubling up with clients or partners. Boosters say that the practice can also streamline the relationship with clients, allowing for quick, functional meetings and cutting down on red tape.Dallas-based Power Public Relations wound up moving in with its client, clinical diagnosis software provider Emerge Clinical Decision Solutions, two years ago after a business lunch."I happened to mention to Scott [Finfer, CEO of Emerge] that we were looking for new office space, and he said, 'We have plenty of space, why don't you just move in with us?' " says Amy Power, CEO of Power Public Relations.Both companies say the move has been a shot in the arm to their culture. "We had no female employees, and they had no male employees, so it helped us create a more diverse workplace," explains Mr. Finfer. Ms. Westervelt is a writer in Oakland, Calif. She can be reached at reports@wsj.com.