How long do the 80 amp and 50 amp strip fuses last on average?

What causes them to fail under situations that just require replacement of the strip fuse to get the car going again indefinitely?

By the way, what difference in performance or longevity between the 50 amp and 80 amp strip fuses?

1979 300D (loop style glow plugs)

Thanks

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1979 300D 220 K miles
1995 C280 109 K miles
1992 Cadillac Eldorado Touring Coupe 57K miles SOLD
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1979 240D 140Kmiles (bought for parents) *SOLD.
SAN FRANCISCO/(*San Diego)
1989 300SE 148 K miles *SOLD