"I cook and you eat."
Translation:Io cucino e tu mangi.
They can't be used interchangeably in most cases. Long explanation first, shorter below.
The phenomenon is called d eufonica. To avoid crazy sounding things like anatre e elefanti or pasta a Ancona you may want to use the magical d eufonica. Try pronouncing those phrases... can you hear the a or e in between? Unless you sound like a GPS, they're probably indistinguishable. This is why the d eufonica is super useful, it helps keep your vowels apart. The rules are relatively flexible. Rule of thumb: if you have trouble pronouncing your phrase without the d eufonica then you should probably throw it in. Sometimes either way is fine, for example, ad ogni modo and a ogni modo are both acceptable.
Here, it can't be used at all because the options following and are voi, tu, Lei, none of which begin with a vowel.
It certainly has a better feel said your way. It gives the phrase more authority and puts the stress on "io" giving it more emphasis than if it came before cucino where it is seems a little weak and superfluous.