So, Socialize in 3E can allow you to do a rather nifty and unique thing:
Create entirely new personas for your character.
It starts as a new set of Intimacies, but can also include having entirely new abilities or even charms.
Rule-wise, the whole thing starts with Heart-Eclipsing Shroud which needs Socialize 5, Essence 3 and has 5 prerequisite charms. Each purchase creates an entire new set of Intimacies called a "Persona". Each Persona is activated with a 4+ hours meditation, and your Personas Intimacies and your real ones are treated as entirely separate things.
The next charm, Hundred-Faced Stranger, gives each of your Personas their own set of abilities.
First, you sum up (Socialize) + (One Dawn-caste Ability) + (Integrity OR Presence) + (Bureaucracy OR Linguistics) + (Ride OR Sail). Your Personas start with that many Ability dots.
Half of those must go into Eclipse- or Zenith-Abilities (So Athletics, Integrity, Performance, Lore, Presence, Resistance, War, Survival, Bureaucracy, Larceny, Linguistics, Occult, Ride, Sail, Socialize).
Personas can purchase Craft, Occult, Lore or Dawn-Abilities, but they may not be higher than your natural ones.
Personas also gain 10 new favored abilities and 3 specialities.
In addition to that, your Personas have half as much experience as you, which may be spent on abilities or specialities for the persona.
And while in a Persona, you can activate any charms you still fulfill the prerequisites for.
The next charm after that allows you to spend Persona-Experience on charms for that Persona.
Further charms upgrade your Persona-Experience to 3/4ths of your actual XP or borrow abilities and charms from your Personas.
Now let's make a character who utilizes that. How about a wandering salesman who can slip into some more appropriate identities in new places?
First we need the relevant charms of course. That spends 7 charms out of our 15 at character creation.
Then we maximize the points our Persona gets. Let's pick Bureaucracy 5, Integrity 5, Ride 5, Brawl 5 and of course Socialize 5. That gives us 25 dots to spend.
The first Persona we create is simply much more outgoing and talkative than we are. Let's call it our "Bard Persona".
Out of those 25 dots, we spend 5 on Brawl to make sure we can still fight properly. We also have Resistance 1 so that Ox-Body technique is still active, and Integrity 3 and Socialize 2. With the remaining points we get Presence 5, Performance 5 and Linguistics 4.
Now whenever we know we want to impress people, we can do so after 4 hours of meditation.
Now let's see how that character may progress.
The first logical purchase would be Legend Mask Methodology, and Draw the Curtain soon thereafter. That's 16 XP spent - so with Draw the Curtain, our persona now has 12 XP to spend and can buy charms.
At Essence 2 (and thus 50 XP) we can create another Persona.
Again Brawl 5, Resistance 1. But this time we make a Thief: Larceny 5, Athletics 5, Stealth 5, Investigation 3, Awareness 1.
Both of our Personas also have 37 XP to spend - enough for 4 charms and something to spare.
At Essence 3, another Persona can be created. We could make a Sailor:
Brawl 5, Resistance 5, Sail 5, Survival 5, Athletics 3, Awareness 2.
Or a Doctor:
Brawl 5, Resistance 1, Medicine 5, Investigation 5, Lore 5, Occult 4. For this, the main character would need Lore 5, Occult 4 - but we could purchase charms with Persona-XP.
And of course there are at least 75 XP to spend on each Persona, which could be 9 charms.
Meanwhile, the characters main experience is well-spent on Brawl-charms which are active across all Personas. If we give the Persona's higher Resistance, the same goes for Resistance-charms.
Socialize-charms are easily shared with the Bard, while buying Awareness-charms would benefit the Thief.
And of course any Solar-XP should be spent on increasing Attributes or Willpower since that benefits all Personas. Or Evocations or Eclipse-charms, since those are automatically shared across all Personas as well.