I have recently discovered a concept of normally placed set by reading R. Engelking's General Topology: The subset $A$ of topological space $X$ is said to be Normally Placed, If for for every open neighborhood $U$ of $A$, there is a $F_\sigma$-set $B$ such that $A \subset B \subset U$.
Now I am curious if there any applications of normally placed sets beyond pure general topology?
Of course, In Perfectly Normal Space all sets are normally placed, which will require the application to involve a somewhat irregular space. For example can be beneficial to prove that some sets are normally placed in the Zariski Topology? or in an infinite-dimensional Topological Vector Space?
Not that I've heard of, it's mostly used in some theory on compactifications, IIRC. Maybe look for the term in MR (mathematical reviews), see what you find. I think, not that much (I don't have access, so I cannot try.)