The thing that differentiates the tactical bag is in its name; tactical. The definition of tactical is combat maneuvers and actions. Typically, the tactical bag is for running a LRRP (long-range reconnaissance patrol) a small, heavily armed reconnaissance team that patrols deep in enemy-held territory. The civilian application would be a light pack with high maneuverability for scouting and supply gathering.
There is no way that you can perform high speed directional changes, reconnoitering, evasion, covert movements, or fish hook maneuver surveillance operations with an INCH or BOB bag on your back.
The tactical bag is designed to allow free movement with agility. It should be stocked with those things that you will need if performing the previously described tasks. It will allow you to overcome most short term, immediate survival challenges for 24 hours or so. The intent of the tactical bag is to allow you to secrete your INCH or BOB somewhere safely. Then you don the tactical bag, and insert into an area where you need to move quickly and stealthily. The tactical bag should allow you to slip freely between abandoned cars and trucks, through tight forest, or in and out of urban areas without catching yourself on the bag.
During major crises there are always roving gangs of people looking to overpower you and take everything that you have. Properly stocked and chosen, the tactical bag will help you escape and evade them. If you would lose the bag you would still have the BOB or INCH hidden safely for you to recover when it is safe to do so.
You should never overlook the possibility that you may have to abandon, surrender, or worse have your bag taken from you against your will. Please read the pack safety article.
It will get you through the first few days until you complete your task and can return home. Whether the situation is a natural disaster, civil unrest, or other event the tactical bag is designed for short term survival and performing surveillance or supply gathering.