Great question! Thanks for your patience in hearing back from me! With the start of school here, it is taking me a bit of time to get back to the board.
The spelling lists in Beyond/Bigger include many of the Dolch words and sight words (which are commonly used words that should be known well prior to proceeding into studied dictation). So while the kiddos are cementing their phonics skills, we also teach the habit of visualizing and spelling correctly a body of commonly used words.

The exercises in the Beyond and Bigger guide are also stepping stones for training a child to hold a mental picture of a word in the mind, which aids in holding the mental picture of an entire phrase/sentence in mind which comes next (when a child begins studied dictation).
This is why, even for children who are great natural spellers and who rarely miss a spelling word, it is wise to go through the spelling exercises as written in the guide. The mental exercises are equally as important as spelling the word correctly. At HOD, we are always looking ahead to the skills that will be needed the following year, and training the child in the guide before for the skills that will be needed in the future!
Blessings,
Carrie