It also depends on who owns the stations. Example:
WTIC-TV (FOX) channel 61 of Hartford is owned by Tribune Broadcasting, Inc. Their "sister station" is WCCT-TV (CW) channel 20 of Waterbury/Hartford. However, if they air a news story from New York City, they'll often use the footage of WPIX-TV (CW) channel 11 of New York City, since that station is also owned by Tribune.
The other big duopoly in Hartford/New Haven is with LIN Broadcasting, Inc. They own WTNH-TV (ABC) channel 8 of New Haven. Their "sister station" is WCTX-TV (MY) channel 59 of New Haven. WCTX-TV airs the 10 PM news produced by WTNH-TV. If WTNH-TV acts on a hot news story from Rhode Island, they'll likely show footage from WPRI-TV (CBS) channel 12 of Providence. Likewise, the same can be said for WWLP-TV (NBC) channel 22 of Springfield, MA. Go to the WTNH website and then either the WWLP or WPRI websites. You'll notice they're virtually identical for that reason.