Solomons and Fryhle has an example in which they have showed a very simple substitution reaction. The question was to synthesize methyl iodide. What they have done is taken methyl chloride and produced methyl iodide in the presence of $\ce{NaI}$ and ethanol through an $\mathrm{S\_N2}$ mechanism. 

Why did they use ethanol? I have read that $\mathrm{S\_N2}$ reactions are favored under polar aprotic solvents and clearly ethanol is not that. Also, since it's a methyl and all substitution reactions on methyl go through $\mathrm{S\_N2}$; so how would it affect my reaction if I would't use ethanol?