Hmm. For the past few years, I've been studying the various tools of planning a story (e.g. beat sheets, outlines, POVs etc.), and I can say that what Terry did here was very clever.
Rather than writing an entire story from the POV of the protagonist (or the assistant, or anyone), Terry alternated scenes - or a sequence of scenes - between characters. Let's take Snuff as an example: the first scene is from Vetinari's POV, then we switch to Vimes, later on to Willikins, and so on.
The scenes, furthermore, alternate between three structures:
1. goal - conflict - setback;
2. reaction - dilemma - decision; or
3. both together.
GCS is simple. You start with the character's goal (what does he want to achieve?), the conflict (what's stopping him?), and the setback (how does achieving the goal set him back?)
For instance, Vimes
wants to avoid going to the country. The
conflict is with Vetinari and Sybil. The
setback is that the people in the Watch are giving him a hard time.
Second, you have
reaction - dilemma - decision. How does the character (Vimes)
react to this "ribbing"? He takes it in stride. Vimes's
dilemma is how to deal with the conflict: He sulks and bridles, for the look of the thing. His
decision, ultimately, is to go along with it.
A scene can be either GCS or RDD, or both together. When they are both together, they develop a character and show him in a new light.

So we see a scene (or two, or three - whatever) from Vimes's POV, then from Willikins's, etc. etc.
Giving the POV to more characters make the story more complicated, naturally.
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As for the Igors, I liked them just fine. As Pterry began to set more stories in Uberwald and surrounds, the Igors became an inevitable part of the landscape.

After all, Uberwald was a homage to the campy horror films of the 50s, so an Igor was vital (pardon the pun).
I have a feeling that Pterry liked Igor after his first appearance in CJ, and so kept him on for TFE and the rest of the series.