McDonald's financial performance may have struggled in the past three years, but it still performs a valuable service, says Warren Buffett's right-hand man, Charlie Munger.

"They take people and give them a first job, which enables them to get a second job," the vice chairman of Berkshire Hathaway told CNBC.

"They do a very good job of educating troubled young people to be good citizens, and they're probably more successful than charter schools."

The fast-food titan has come under criticism — along with many other companies — from labor activists over the past few years for low wages. McDonald's recently increased the minimum wage at its company-owned restaurants to $10 an hour.

Meanwhile, McDonald's new CEO Steve Easterbrook, announced his turnaround plan for the company Monday. That includes a restructuring of the company into four units and a move to sell 3,500 of the restaurants owned by the company, which has 36,000 outlets in total.

"Progress will be bumpy and uneven," Easterbrook said.

McDonald's stock has generated a total return of just 0.2 percent in the past year, compared with 14.2 percent for the S&P 500 index.

Morningstar analyst R.J. Hottovy said last month that Easterbrook is moving in the right direction. Still, "investors should not expect an overnight turnaround," he wrote on Morningstar.com.

"This is particularly true in "priority markets" such as the U.S., Germany, and Japan, and we anticipate negative comparable sales trends to persist across 2015."

McDonald's can gradually return to the lower end of its long-term financial targets — 3 to 5 percent system sales growth, 6 to 7 percent operating income growth and returns on incremental invested capital in the high teens, Hottovy said.

That's because of the "wide moat derived from strong brand awareness, convenient restaurant locations, and significant bargaining and advertising scale," he explained. "However, we also believe a McDonald's overhaul will be a multi-year process requiring significant time and resources."

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