I was just curious and quoted the heritage use of aux sends in conventional consoles. There is no reason to use this schema in software.
If the effects are dedicated part of a sound I would put it into the same rack - like an insert effect. Reverb is indeed a candidate for aux send.
Remember that aux sends in Cantabile can be - unlike usual mixing consoles - freely routed to other racks. Probably you can resolve some problems already without more aux sends.
Concerning number of aux sends my personal opinion is more than 4 would be easily confusing, but that's just me...
With reworking the audio bus I wasn't about technical changes, just better and more intuitive gui access.