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.Glacial Fortress supports white-blue decks by supplying either color from one land. It enters untapped when you already control a Plains or an Island, so its performance depends on the types represented by your earlier land drops. A basic or a typed nonbasic can satisfy that requirement. This makes it particularly useful after the first turn, when the mana base has begun to establish itself.
Hallowed Fountain is a useful partner because its basic land types can enable the untapped entry. Flooded Strand can find that shock land or an appropriate basic first, setting up a later Glacial Fortress. Sequencing those sources in the right order can preserve mana for development and interaction without paying life for this land itself.
For control and blink strategies, the practical benefit is choosing between spells such as Swords to Plowshares and Counterspell as the turn develops. White removal and blue countermagic ask for different colors at different moments. A blink deck also wants to cast its white creatures without losing access to blue protection for the engine. A flexible source supports those decisions without requiring a separate fixing artifact to stay on the battlefield.
The entry check uses land types rather than names or the colors a land happens to produce. Glacial Fortress has no basic land types of its own, so a fetch land cannot search for it. An opening hand built only from lands with similar conditions may start slowly. Keep enough reliable first-turn sources to make the condition easy to meet.
