I think FAR 135.243 might explain why 1200 is a magic number:
(c) Except as provided in paragraph (a) of this section, no certificate holder may use a person, nor may any person serve, as pilot in command of an aircraft under IFR unless that person—
(1) Holds at least a commercial pilot certificate with appropriate category and class ratings and, if required, an appropriate type rating for that aircraft; and
(2) Has had at least 1,200 hours of flight time as a pilot, including 500 hours of cross country flight time, 100 hours of night flight time, and 75 hours of actual or simulated instrument time at least 50 hours of which were in actual flight; and
(3) For an airplane, holds an instrument rating or an airline transport pilot certificate with an airplane category rating; or
There is no minimum time for SIC:
§ 135.245 Second in command qualifications.
(a) Except as provided in paragraph (b), no certificate holder may use any person, nor may any person serve, as second in command of an aircraft unless that person holds at least a commercial pilot certificate with appropriate category and class ratings and an instrument rating. For flight under IFR, that person must meet the recent instrument experience requirements of part 61 of this chapter.
It's been a long time since I flew Part 135, but generally wet behind the ears SIC had a problem because they couldn't upgrade to PIC for at least a year. (1200-250=950 hrs max FAR 135 is 1200 hrs/year)
Originally Posted by Velosprints
Thanks lr31apilot. I was talking to someone who said that 1200 hours helps with insurance costs. But I guess it differs from company to company, or perhaps by insurance company.