Platinum is used because it works acceptable for the warranty period. Platinum works equally well as a fine wire plug except does not last as long as a fine wire iridium.
Since you don't get to pick which plugs come from the factory, you should consider how often you are going to replace the plugs. If the vehicle burns oil for example you are going to need a shorter replacement interval and may be wasting money on iridium. If it does not, it is arguably worth using iridium on the first plug change.
On subsequent plug changes, 2nd/3rd/etc, I'd just go platinum fine wire and change them more often. It's good not to leave them in too many years so they aren't seized in place and to examine for hints of an engine problem. At least that is my strategy, I tend to get newer vehicles every few years so the older a vehicle gets the fewer miles are put on per year so the more years before X # of miles would otherwise wear out spark plugs, then with either type it has been long enough that I'm replacing the wires while I'm at it, and on some vehicles with a coil on each plug, it may be time to replace the coils too... replacing something old before it fails can be cheaper than a tow, but of course there is only so much it's reasonable to do but I'm talking about well over 100K mi by that point.