I believe the question re: channels 3 and 4 are more for those devices using RCA connections (the yellow, red and white cables) like VCRs and DVD players that required the user to change to channel 3 (usually) or 4 in order to watch. This may also be needed by some older cable boxes.
If you choose "no", it just will not reserve or program these during the scan. If you select "yes", these two channels will be included in the scan and will just appear blue or be filled with static unless using with one of the above devices requiring 3 or 4.
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