Both increase
throat hit. I advise against adding them if you mix juices at the higher end of the nic spectrum(18+mg/mL) unless you like being punched in the
throat. jk
The former also acidifies the mix and quite possibly turns the nicotine into its acetate
salt form, which is not as readily absorbed as its freebase form.
Some people add acids to preserve flavor. I used to, but it didn't seem to do much so I stopped doing it.
Other people like to add PGA(alcohol) to their mix to thin out VG.
These subjects have been covered extensively in multiple threads throughout the DIY section. I recommend checking out the vinegar thread.