Splicing is predominantly (but not exclusively) used for creating very strong and durable knotless loops at the ends of rope.
Google "splicing with a marlin spike" for plenty of info.
There is even a marlin spike knot, for temporarily securing the marlin spike to guard against loss when you need your hands to be doing other things.
A metal marlin spike is actually for working with wire rope while, traditionally, a wooden tool called a Fid (looks like a large sewing needle) is used for working with natural and man-made ropes.
Showing my age a little - I learned that in the scouts as a kid, back when the scouts were allowed to teach you stuff like that
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