It definitely comes up in search-index style posting lists. For dense postings you'll usually deal with bitmaps, but you'll have sorted integers for sparse ones

It definitely comes up in search-index style posting lists. For dense postings you'll usually deal with bitmaps, but you'll have sorted integers for sparse ones and you usually have at least one list per search term. There's all sorts database indexing problems that can use this too, I'm sure.