We have vacuum waste systems for several reasons. Less weight and they do not smell as bad. Old blue water systems are horrible. The days of stupid pax dropping junk in them that clogs the systems are done.
The vacuum waste system uses about 5 oz of water per flush if I remember correctly.
Negatives.
As said above, if the jet pumps go out you need to rely on altitude for a vaccum system. One point waste usually dual tanks, I once had a dump valve break both tanks were dependant on this valve, this was a grounding and really shiiy experience.
Blue water, they stink, they jam they need more maintenance and servicing.
I work on freighters, they are all blue water. It is the ideal system for an aircraft that only has crew using them but they still stink!