The Shard Salvager skill allows Aloy to disassemble excess resources and modifications for ~50% of their metal shard value. This skill only applies to resources that can be sold to merchants. Items can be salvaged one at a time or in multiples. Once disassembled, items are permanently deleted and cannot be restored.
This skill comes in handy when Aloy's resources satchel is full, as space can be made by transforming unneeded items into metal shards. It is also useful in Ultra Hard difficulty, where every shard matters.