VectorUtil#squareDistance is used in conjunction with VectorSimilarityFunction#EUCLIDEAN.
It didn't get as much love as dot products (
LUCENE-9837) yet there seems to be room for improvement. I wrote a quick JMH benchmark to run some comparisons: https://github.com/jpountz/vector-similarity-benchmarks.
While it's not as fast as using the vector API (which makes squareDistance computations more than 2x faster), we can get a ~25% speedup by unrolling the loop in a similar way to what dot product does.