(1) In terms of ratings, reruns are a surer bet, especially during summer

   The assumption that summer reruns are bad for TV is accepted research wisdom. As Media Life’s Toni Fitzgerald reported in May, a Magna Global USA study from 2003 showed that “broadcast household ratings dip 11 percent on average when repeats make up 20-to-40 percent of the primetime schedule, and 20 percent when reruns account for 40 percent or more of all network shows.”
   But the study does not take into consideration that the fact that many viewers leave town during spring break, summer and Christmas—the times of year when TV schedules are traditionally rerun-heavy. 
   The fact is that a summer rerun of an established series is more likely to win its time slot than a new episode of an inferior show.
   We've seen this again this summer. Despite aggressive ad campaigns for “North Shore,” “Casino” and “Trading Spouses,” Fox is still finishing a distant fourth on Monday nights among households. 
   CBS continues to rule, even with reruns of "CSI: Miami," “Everybody Loves Raymond” and the rest of its comedy block.
   The same holds true for Tuesdays. Not even the presence of Barry Levinson could save “The Jury” from “Navy NCIS.”
   True, certain shows will fare poorly in reruns during the summer, but in general the opposite holds true.

(2) Reruns sustain franchises

   A network is usually better off airing reruns of an established show during the summer rather than pre-empting with original programming, and not just because the rerun might bring in better ratings.
   Reruns are great for sustaining and building a show's franchise, as smart programmers are well aware.
   For one, a show's core audience will stick with it during reruns out of loyalty. They'll want to see favorite episodes again, or perhaps the one or two they missed.
   Too, summer reruns give fans who discovered the show at mid-season a chance to catch up on the earlier episodes they missed. And of course reruns also work to snag new viewers to a series.
  Yes, it's possible to overexpose reruns, which is a huge turnoff. But reruns in themselves are not the fault.
   We saw how smart use of reruns worked for CBS  in June, when it repeated “CSI” and “Without a Trace” in the Thursday 8 p.m. time slot normally occupied by “Survivor.”
   We'll see it again in the fall with CBS's “Crimetime Saturday” hour. Borrowing from the HBO playbook, the network will use the Saturday 10 p.m. slot to air encore presentations of “CSI,” “Trace” and the spinoff series “CSI: New York” for the benefit of those who may have missed those shows earlier in the week.

(3) Reruns give viewers a break

    Part of the problem with the 12-month TV schedule is that it assumes that viewers will always be around to watch.
   But even the most hardcore viewers need a break, especially during the summer. That's one big reason we have summer reruns.
   Say you plan your life around “NYPD Blue.” You still have another life, one relating to family, and you need a few weeks off, usually in July and August, for that other life, if only to take care of obligations accumulated earlier in the year when you were glued to your TV set. 
   Hard as it may be for TV executives to believe, people actually do things besides watch television. Even the strongest of networks can only expect to grab so much of a viewer’s time.
   The risk is with being greedy.
   Rather than attempting to lock in viewers for 12 months a year, it makes more sense to focus on the nine or 10 months when viewers are most inclined to be watching.
   HBO gives us the model for that. Rather than competing with the other networks seven nights a week, HBO concentrates on one night of original programming, Sundays, using reruns of those shows throughout the week to build toward next Sunday.

(4) Reruns provide solid bricks whenever there’s a hole in the schedule.

    The other fallacy about the year-round schedule is that it assumes the networks will suddenly start exercising patience with new shows.
   Patience is a virtue but certainly a rarer and rarer one over the last 25 years of television.
   Back in the days of three networks, even the lowest-rated show was guaranteed 13 weeks on the air. No more. Now if a show fails to pull viewers after one or two weeks, it gets yanked.
   That leaves the network with a hole in its schedule.
   How does it plug the hole?
   It can plug it with specials or a replacement show that’s already in reserve. 
   But unless the network has an exceptionally deep bullpen--none do at this point--it has little choice but to slip in a rerun.
   Imagine you are Fox, the very network that set out to launch the 12-month schedule earlier this year.
  Suppose Tuesday night placeholder "House" fails to take off in November. 
   Do you move up the launch of another show to fill in for it? 
   For strategic purposes you probably want to wait until January to launch a new show, paired with “American Idol." 
   In that case, as at Fox you have few options, and the most logical is the one networks have been relying on for years: Toss in a rerun.
   You'll still be able to talk about the 12-month TV season, but you'll be doing the smart thing by turning to one of traditional television's more reliable devices.