There can be reasons for looking at specific fare buckets. Promo eligibility and fare changes from rebooking come to mind. Mostly, though - for the reasons outlined by LBJ - you're just wasting your time. Use ITA, Orbitz, Kayak, whatever to find & price itineraries. In their search logic they will account for adv purchase/min stay/max stay/routing rules/fare bucket availability for available published rules, and married segment routines.

If you have real flexibility in your travel dates checking for the lowest published fare and picking dates & duration to fit can be an excellent trick. Hence the lamentation of the loss of ExpertFlyer for Delta...