On NH44 and NH48, backups are usually another plaza or a town CCS2 a few kilometres off the polyline. Use them when the primary has one gun, a closing time you cannot prove, or a rating that looks like a parking-lot charger. Swap before you leave, not after you have already burnt the detour budget.
On Konkan, ghats, and parts of the Northeast, the next site may be 80–120 km. Then a backup in the same cluster is the only backup that still exists. If EV Grids only offers a pin 40 km backward, that is information: do not enter the thin stretch at 22% hoping regeneration will invent a gun. Charge on the dense side first.
Chain checks exist because stop two moves stop three. A cheaper site that sits later on the drive can strand the following leg below reserve. When the UI offers Fix trip, it is telling you the new arrival percentages. Read them. A 4% cheaper kWh is not a win if Chandigarh or Panaji is then a 9% crawl in traffic.