Synaesthetes have much better memories than other people, though largely for things involved with their synaesthesia. To understand this, consider a situation in which you’re trying to remember someone’s name. Is she Betty or Veronica? Now imagine that, to you, B is blue and V is purple. You can remember that woman in question had a purple name, and therefore it’s more likely that she is called Veronica.
As you are also more likely to get a favourable response from someone whose name you can remember than someone whose name you can’t, synaesthesia might actually help social relations in some situations. Even further, synaesthesia might offer some protection against age-related memory decline because a synaesthete has more than one “route” by which a memory can be accessed.
Synaesthetes also tend to be better at mental imagery than other people, again with the restriction that this appears to be related only to aspects of mental imagery involved in their synaesthesia. Mental imagery might not seem hugely useful, but we actually use it a lot in our everyday lives – to remember faces, to navigate, even to put together recalcitrant IKEA furniture.
Synaesthetes are more creative, in some ways, than other people. Creativity can be broadly categorised as either convergent (bringing together disparate ideas to make a new whole) or divergent (thinking up entirely new ways to use existing items). It’s the former of these that synaesthetes tend to excel at, and they also spend more time engaged in art and music than other people.
Edhubbard at English Wikipedia, CC BY-SA
Synaesthetes might also have a different personality profile from the rest of the population. On the “Big Five personality test”, which measures five aspects of personality (openness to new experiences, conscientiousness, extraversion, agreeableness and neuroticism), synaesthetes score lower on agreeableness and higher on openness. Synaesthetes also have more unusual experiences and are more prone to disorganised thinking than other people.