When to use sub-brackets for similar instruments within a section?

Question

In some scores, especially printed sheet music, “like” instruments in larger sections will be grouped together with sub-brackets, such as piccolos with flutes, oboes with English horns, clarinets and bass clarinets, etc. Here’s an example, cropped from a photo of one of my sheet music books (“Theme from Jurassic Park” by John Williams, published by Hal Leonard):

I’ve been Googling and reading various theory references, but I can’t find any clear indication of when sub-grouping like this should or shouldn’t be used. Some sources recommend it, others don’t say a thing.

Is there any consensus for when or where sub-grouping like this should be used, or is it a stylistic choice?

Answer 1

Elaine Gould in "Behind Bars" (the standard reference for modern notation) writes:

A thin square bracket is recommended as a secondary bracket for joining the following staves:
- two or more like woodwind and brass instruments; alternatively, two or more of the same instrument
- two staves and/or additional lines required by a single percussionist for different instruments
- like voices
- a divided string line

So they are optional, but recommended.

The decision to use them or not should be dictated by the consideration of what is clearest for the conductor (as should any notation choice).

Answer 2

The 'sub-brackets' simply group together families of instruments - the flute section, oboe section etc. It helps add clarity for the score reader in orchestral pieces.