(b) If you chose to pay this spell's impending cost, it enters the battlefield with N time counters on it
In Magics most powerful regularly played competitive format, Legacy, where a low total mana value means that decks play less lands, this is a fantastic tool for making sure you can find your next land drop if you kept a hand with only one or two

Madison Li 1 Liberty Prime, Recharged 1 Automated Assembly Line 1 Brotherhood Scribe 1 Overencumbered 1 The Prydwen, Steel Flagship 1 Sentry Bot 1 Dweller's Journey 1 Curie, Emergent Intelligence 1 James, Wandering Dad 1 Nick Valentine, Private Eye 1 Synth Infiltrator 1 Assaultron Dominator 1 The Motherlode, Excavator 1 Plasma Caster 1 Synth Eradicator 1 Arcade Gannon 1 Electrosiphon 1 Red Death, Shipwrecker 1 Rex, Cyber-Hound 1 Sentinel Sarah Lyons 1 Shaun, Father of Synths 1 Sadistic Simulation 1 Brotherhood Vertibird 1 T-45 Power Armor 1 Ferrous Lake 1 HELIOS One 1 Austere Command 1 Open the Vaults 1 Mechanized Production 1 One with the Machine 1 Wake the Past 1 Mystic Forge 1 Panharmonicon 1 Solemn Simulacrum 1 Steel Overseer 1 Clifftop Retreat 1 Exotic Orchard 1 Glacial Fortress 1 Irrigated Farmland 1 Prairie Stream 1 Skycloud Expanse 1 Spire of Industry 1 Sulfur Falls 1 Temple of Enlightenment 1 Temple of Epiphany 1 Treasure Vault 1 Paladin Danse, Steel Maverick 1 Nerd Rage 1 Robobrain War Mind 1 Bottle-Cap Blast 1 Elder Owyn Lyons 1 Behemoth of Vault 0 1 C.A.M.P

While the one mana instant is certainly very powerful and flexible, especially in the current ETB-heavy metagame, it does nothing on its own
As you can see, indestructibility isnt just about defenseit can also enable powerful combos
More recently, theres The Archimandrite from The Brothers War Commander that gains you life on upkeep based on the number of cards in your hand