Mark Lambert spent 12 years working at Fortune 500 companies. For the past eight, he’s been plying his trade at small start-up ventures. He prefers the latter, and it’s not a close call.

An experience Lambert had shortly after joining ClearSlide, a maker of sales-productivity software tools where he has been CFO since May 2012, illustrates why.

“Smaller is better because there’s more fruit for your efforts.” — Mark Lambert, CFO, ClearSlide

The company’s founders suddenly decided to raise a second round of equity financing immediately instead of late in the fall, as per the prior game plan. The rationale was sound: Market conditions were favorable and there was strong interest from top investors. But it required fast, intense action by Lambert. He had to prepare an upgraded financial model with historical actual results, three years of projections and a pile of metrics that are particular to software-as-a-service businesses.

At that time ClearSlide’s entire finance and legal team was three people, including Lambert. “I opened up a blank Excel workbook on the morning of July 4 and started clicking away,” he says. Late that afternoon he shared the model with the founders, and within two days “it was locked,” just in time for the first meetings wth investors.

“That’s not an uncommon experience for start-up CFOs,” Lambert says. “Direction can change very rapidly at young companies. To be successful, financial leaders have to be flexible and energetic and enjoy the challenge of accomplishing a lot in a short amount of time.”

But the appeal is not all about getting high on speed, so to speak. “Smaller is better because there’s more fruit for your efforts and you get a real seat at the table,” Lambert says. “The most exciting opportunities are the ones that stretch you beyond your comfort zone, and that’s what you get at a start-up.”

Ironically, he first recognized his strong interest in start-ups while heading finance for the search business at a large company, Yahoo!, where he worked from 1999 to 2006. In 2002, when he came to the search unit, it was a small operation. After four years of product development, aggressive hiring and two big acquisitions, the unit surpassed the $1 billion revenue mark.

“I remember when we had our first million-dollar week, then our first million-dollar day, then the first week when we strung five million-dollar days in a row,” Lambert says. “That kind of excitement stuck with me and got me interested in being part of a founding team, building something from scratch and helping set the direction, and growing it from an idea to a big business.”

When he was recruited for the vice president of finance role at startup voice-services company TellMe Networks in 2006, it wasn’t a tough sell. There too, the game plan changed quickly after Lambert’s arrival. The company, which had been on an IPO track, instead was acquired by Microsoft in 2007.

Next came Lambert’s first full-company CFO job, at Connexus, an online advertising and social-media company. Shortly after arriving there in 2007, he made a strong recommendation that the company shut down its largest business unit, because of its low margins, and focus solely on brand advertising.

“It wasn’t sustainable,” he says of the low-margin unit. “Closing it was not a popular idea and a lot of people were very nervous about it, but the board implemented it and over three years we improved our margin and our revenue. And because of that, we had a successful exit,” a sale of the company to Epic Media Group.

Aside from Yahoo!, the large companies on Lambert’s CV include 3Com, Kaiser Aluminum and Gap Inc. While start-up ventures are closest to his heart, he says the experiences at the other end of the size spectrum provided necessary education. “You learn about process and policies and internal systems. Because of that experience I have a varied background across finance, M&A, operations and strategic planning. That helped create a good balance for me moving forward.”

At ClearSlide, Lambert is spending a lot of his time working with the sales team, reviewing large deals and helping negotiate contracts. Sales operations reports to him, and of the company’s 210 employees, about 150 are salespeople.

But his job is still diverse in terms of its functions, which is something he enjoys. In addition to finance and sales, he oversees legal and facilities. “On a given morning I might be in the boardroom in the morning, helping set company direction, negotiating a sales contract for two hours over lunch, and looking at potential new office space in the afternoon,” he says.

Indeed, he says, some of the things most on his mind are real estate, general recruiting across the company and designing effective incentive sales compensation, all because of ClearSlide’s fast growth pace.

“Not many people can say they started with something small and grew it into a massive enterprise,” he says. “That’s really motivating. If you’re only going to have one career, try to be part of something big.”