Chicken?????
I knew Peely was about and he is a bit of a technical buff, so I wanted to make room for his expertise to shine.
Heather, my theory is that sight rhymes have come about because English is a language that has so few rhymes ( Italian and French for example have plenty of rhyming endings )
I think we all know how frustrating it can be at times, trying to find a rhyme and use the word that we need to use, and sight rhyme is one device to extend the number of rhymes available.
The book that Peely referred to ( Stillman, The Poets Manual ) calls this type of rhyme, spelling rhyme and gives examples such as love/move, find/wind ( the blowing wind )
bough/though.
I have no interest in using this device, I think it seems too forced and distracting.