If one uses halides that are sterically hindered with accessible protons in the beta position, the alkoxide in this reaction with act as a base, especially if it's bulky, and an elimination side product will result.  
If one uses halides that are sterically hindered with accessible protons in the beta position, the alkoxide in this reaction with act as a base, especially if it's bulky, and an elimination side product will result.  If this happens, the hydroxyl group on the alkoxide will just reform and a useless separate alkene will form.  The goal is to have the deprotonated oxygen attack the halide in nucleophilic substitution, kicking off the halogen, and attaching itself to a new carbon chain.  FTP, name this reaction that prepares molecules of formula R-O-R, known as ethers.
If one uses halides that are sterically hindered with accessible protons in the beta position, the alkoxide in this reaction with act as a base, especially if it's bulky, and an elimination side product will result.  
Williamson ether synthesis