Pros and Cons of sometimes using a separate app (vs. adding to existing app)?

Pros and Cons of sometimes using a separate app (vs. adding to existing app)?

Could we use this post to collect wisdom on the behavior / capabilities / strategy of adding more as a separate app vs. adding to the same app?   I'll give a start from our limited understanding.  I haven't seen this discussed in the Help or on the Forum -but please provide links if it is.

(We have a "main" app with a suite of some 30 tables/forms and associated reports, etc.  But for 2 others, we've made each separate apps, mostly for their own unique security -Enterprise license- and unique customer Portal. But we are wondering about potential negatives to being separate apps.)

SEPARATE APP: Behavior/Benefits
  • Distinct Roles (in case the hierarchy needed for this app is very different and being aware that a User can only be assigned to one Role).
  • Distinct Profiles and Users from the main app.  (May provide security that is simpler or gives peace of mind re: accidental access?)
  • Distinct Customer Portal
  • (Even though a separate app, can still use Lookups from forms on the other app.)
  • ... More...?
SEPARATE APP: Negatives/Caveats
  • The obvious: Will be a separate "My Apps" dashboard choice, and the tabs will not include those of the main suite. 
  • The extra maintenance of separate Users, Roles, Profiles and maybe some duplicate scripts.
  • Although Lookup fields can be to forms in another App, it seems that deluge scripting cannot directly access the other app?? (except via Functions - and I'm not familiar with this or its caveats).
  • ... More...?
Please add, correct, clarify, and improve - thanks!