This is the classic explanation. A bit long though, I think there are some decent examples on youtube if you go looking.
Good deinterlacing takes you from "bruh I hate interlaced content, PS2 is sucky" to "the fuck was I even complaining about?" Like I can barely tell when games are interlaced over the FM, you have to really know what to look for or go into the menu and check. Seriously, it has the same effect that good scalers have on 240p content, just making the games enjoyable again... no more distracting rat teeth, no more blurry mess in motion, no more flicker, no fiddling with GSModeSelector or bootsy emulators, just pop in the disc and enjoy.
If your TV handles interlaced content well I can see the passthrough on the OSSC being a good option. I don't know what your playing but I can't think of a single 480i-only game I own where it isn't worth the added latency.