The conjunction come serves as well to compare two data. We have already spoken about comparison and we have learnt that di and che are used as comparative particles. Let's repeat briefly the different types of comparison and let's see than when come is used in this context.
If the comparison is done on a pronoun (personal pronoun, demonstrative pronoun) or a noun with an article or specified otherwise the comparative particle is di. If the comparison is done on a whole sentence the comparison particle is che.
comparison for superiority
Lui è più grande di me.
He is bigger than me.
Lui è più grande di quello.
He is bigger than this.
Lei è più grande di Maria.
She is bigger than Maria.
comparison for inferiority
Lui è meno grande di me.
He is not as big as I.
But is the comparison is done on a whole sentence the comparison particle is che.
È più facile leggere un romanzo che scriverne uno.
It is easier to write a novel than to write one.
comparison for infiority
Oggi fa meno freddo di ieri.
Today it is less cold than yesterday.
Now you may ask for what come is needed in comparison, if it doesn't show up in any of the examples before. The answer is simple. One comparison lacks, the comparison for equality. The comparison for equality is done with come.
Per i miei gusti non è così bella come tutti la descrivono.
To my taste she is not as beautiful as she is described by everyone.
Nella prima metà del ventesimo secolo la scienza giunse alla conclusione che l' Homo Sapiens non è così intelligente come si pensava.
In the first half of the twentieth century science came to the conclusion that the homo sapiens is not as intelligent as it was thought he is.
In the context of a comparison for equality come is a comparison particle and not a conjunction because in this case it doesn't establish a relationship between two clauses.
Come can be a conjunction as well if the clause introduced by come explains the way how something is done.
Dovrei tapparmi le orecchie come fanno loro quando i loro bambini gridano.
I should hold my ears like the people do when their children cry.
If the comparaison is hypothetical the congiuntivo come corresponds to the English conjunction as if. In this case the action / event described in the subordinate clause is hypothetical and not real.
Mi sento come se non dormissi da due notti.
I feel as if I didn' t sleep for two nights.
Parla come se ne sapesse qualcosa.
He speaks as if he knew something about it.
Those who speak Spanish may be induced to believe that come is also used to reveal a casual relationship.
Como no le entendí le dije que vuelva más tarde.
Because I didn' t understand him I asked him to come back later.
In this use, as a casual conjunction, come is very, very rarely used in Italian and if it is used like that, it seems to be a spagnolismo. Considering that in Italian there is a big offer of casual conjunctions (poiché, perché, giacché, visto che, dato che, dacché) there is no need to use it in this context.
