I have several with time-varying bonuses (Discover and at least one other change their bonus categories quarterly and there are other specials for other cards). Beyond that, many of the bonuses have caps and other interactions (e.g. sometimes Discover's bonus on Amazon transactions is better than the original card). Something that manages the transaction routing for me is valuable, even beyond consolidating cards.

Card rules vary frequently, down to daily. Also, many rewards have limits (both min and max). Wallaby helps you keep track.

My Citi card has special categories that give me double cash back every few months.