In the mid-2000s, FireWire was great for external hard drives. You can get yourself a FireWire-to-SATA enclosure and put a good large SATA hard drive in it for external storage.
Also, in addition to importing MiniDV or Digital8 tapes, if you have any analog home movies shot on VHS or Video8, you can get a FireWire digital video converter (such as the Canopus ADVC-55 or -110, ADS Technologies' Pyro A/V Link, Dazzle's Hollywood DV Bridge or the old Pinnacle MovieBox DV) to digitize the analog video. Or if you have a MiniDV or Digital8 camcorder that supports AV-to-DV passthrough, you could use THAT as a FireWire digital video converter.
FireWire is also great for Target Disk Mode on older Macs.
Since my retro iMac G3 for running old games is too old to get online, even with Ethernet plugged in, and since it currently just runs Mac OS 9, to share files I'll hook up a PowerBook G4 running Mac OS X (like this one running Tiger) to the iMac booted in Target Disk Mode via FireWire and use that to transfer files. (I can transfer files between the PowerBook G4 and my M1 MacBook Air over the network, though.)
But yeah, back in the 2000s, most Macs on the market had FireWire, while only a handful of Windows PCs did (usually with desktop towers you had to get a PCI FireWire card for them). And now history is repeating itself with Thunderbolt, the protocol that replaced both FireWire and MiniDisplay on the Macs (to the point where Apple came out with a FireWire-to-Thunderbolt adapter, and the aforementioned Target Disk Mode was revised to also work with Thunderbolt). All Macs currently on the market have at least one Thunderbolt USB-C port, while only some Windows PCs do (usually they'll have at least one regular USB-C port, but it's rarely the Thunderbolt variety).