It would skip a trip to the Elemental Sanctuary, the Moblin Fight in north hyrule field, and the Ezlo backstory cutscene that comes immediately after. I'm not exactly sure how much time it would save, but it would be quite a bit and is probably the biggest (reasonable) skip currently left in the run.

That said, afaik early cape wouldn't really offer anything. Theoretically if we could get the cape before entering crenel then we could do bootsless swamp trivially and get the Ocarina before Cave of Flames, letting us do a faster route there. However, in order to finish Palace we need either the cane or the ocarina (which would require cutscene OG) for a small key, as well as either the magic boomerang or the lamp for boss door clip, meaning we'd need to leave palace after getting the cape which I can't see ever being faster. The only other dungeon where cape could save time is in Deepwood, but fusing is locked behind beating Deepwood so that's impossible. Still, the extra sanctuary trip + cutscenes is a pretty big timesave on its own. Although it would require beating Gyorg without clones which is awful, so maybe don't find that ^^