Efficiency of the lookup formula

I have some question about how efficient the lookup formula is

I have a situation where we when we have new items have the ability to give that item a mapping to another item to pull some initial data for since we don't have anything for it yet.
we used a lookup instead of just repopulating the initial data so the users can change there decision quickly themselves.

we have a formula like this for the item mapping, which because 99% of our items don't need mapping it ends up lookup up itself. it doesn't seem efficient to me,

but the alternative to leave the unmapped blank and have an if statement, checking for blank and only lookup when there is a value else pull just pull the value.

Which one is more efficient, or is there a better way of doing this

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