I've just picked up PEG Inc's edition of "Savage Worlds," and the way experience works for me is unclear. Each player controls a Wild Card character and collaborates on controlling a pool of Extra characters. At the end of a session, the GM awards XP to the players. Each player gets the same number of XP, from 1 - 3, based on how the group did/how much they accomplished. These points are then spent on characters. The assumption, presumably, is that players will spend these points on their primary, Wild Card, characters. Can they choose to spend the points on the Extra characters, though? Say the group has a trusty retainer who is a constant in the campaign. Can the retainer be given experience? I suppose the only reason one would do this is to attain the eventual goal of gaining edges for the Extra, which would be risky (given that the Extra is eliminated if Wounded)...
No, the end-of-session xp award if for PCs only. Extras advance in a different manner.
SW Deluxe Edition p 43:
While that says nothing about their advancement, it most assuredly sets a certain attitude.
SW Deluxe Edition p 81:
That is - roll to see if the allies levelled up whenever you feel like they had a chance.
In most cases, where a Mook (aka Extras) just need a stat roll, making it up on the fly works.
@Jeor Mattan's answer really is reflecting a NPC / Mook / Extra that is effectively part of the Team. For example, the long term retainer (eg. Alfred in Batman). The Squad of Soldier's that work with the PCs on a regular basis.
In other words, retainers where the PCs would expect to see development in.
For the average smuck on the street, they simply don't level, unless the plot calls for it.
Now, on the other hand, if I am creating a NPC villain and I want my PCs to have a good challenge. I'll throw X number of mooks, and a couple of villains which I hand craft using the character creation rules as a GUIDELINE. Overall, I character model, but don't worry about the details too much on the villains. I use the character rules to try to prevent the villain from being too overpowered.
I might add an extra edge, and a couple extra points, but that really challenges the characters, and only takes a few minutes. But I only do that for villains or NPCs where the PC's will be seeing them on a regular basis or where I want them to be nervous about the fight.