I can’t speak for network correspondents/anchors, but at the local level anchors (those meat puppets who sit behind the desk and read the news) spend their non-air time reading the wire services/newspapers and writing scripts. Larger markets require less of this since they can hire writers; smaller markets need their personnel to wear more than one hat. Anchors, as a rule, don’t report in the field. This is not universal, however.
Reporters/correspondents work in the field. They generate, research, and conduct the field work required to put a story on the air (interviewing, writing, voicing their track). These folks spend their non-air time on the phone, in the field, writing, voicing and sometimes consulting on the editing of the piece.
Anchors have been known in the past to spend less time in the office (usually in the form of a long lunch) but, it’s a leaner, meaner business now and most stations have a bottom line they’re trying to maintain. The high priced help have to do more since there are fewer people working behind the scenes.
Also, the anchors record promos that air between programming to entice you tune at 11 (10 central). Sometimes, there are live promos as well, particularly when there is breaking news.