Just that really. My dd (year 1) does and they get on my nerves just with the amount of words she wouldn't use in her writing yet...for example leisure, pleasure, beige...I get keywords/tricky words or words used a lot but surely if they don't use the words a lot at that age it is a bit of a waste of time.
Maybe I am wrong and be happy to hear if you think learning/testing spellings is very important.