Why are 'table salt and sugar are both terrible candidates for recrystallization'? I received a comment on one of my other chemistry questions stating that


  table salt and sugar are both terrible candidates for recrystallization, albeit for different reasons.


Why are salt and sugar terrible candidates for recrystallization?
The solubility of $\ce{NaCl}$ has very poor temperature dependency. If you dissolve it at $100^\circ\rm C$ and precipitate at $20^\circ\rm C$, you'll essentially lose about 35 g to purify 3 g. Even using a fridge, you'll still lose more than half of the product, which is quite a bad business. Industrial process relies on evaporation, I think.

Sugar is another story. It does have a nice temperature dependence, but it dissolves too well, even when cold. Just imagine dealing with that awfully viscous syrup, like molasses. It would take forever to filter, and quite a while to crystallize. Industry can handle that, but for home chemistry I'd suggest something more pleasant.