*sneaks in* Hope you all had nice holidays.

As for the question:
YurigirlzCrush wrote...
so now a question that's on topic! *grins* what are everyone's thoughts on sections from the perspectives of the bad guys?
I don't want to give away too much, and I'm not sure I could sell the bad guys as being both bad and realistic (since I'm not a mean person by nature and I don't know if I could really sell their villainy as both necessary and believable).
but I've been thinking some sections I have in my story for providing certain bits of info might be better if I rewrote them from the side of the bad guys instead. it would mix things up a bit and maybe I could sprinkle at least hints of the villains and their motives into the early parts of the story. so I wanted to find out other people's thoughts on sections from villain perspective and any particular traps to avoid in them.
"Both bad and realistic" is a tough sell for me. It is a rule of thumb for me that my villains need to be just as developed as my protagonists, if not more. And I like to think that
1. The villain is the hero of their own story, and
2. There is no are no "bad" or "evil" goals, only goals that conflict with the protagonist's. I think most storytelling has eschewed the mustache-twirling, steal-your-damsel "I am the bad guy because I am bad" villains.
Look at real-world conflicts: for example, a conflict between a stable country with nuclear capability surrounded by allies and an unstable country trying to develop nuclear capability surrounded by enemies, against a backdrop of world-wide nuclear proliferation deterrance. The "villain" is all a matter of perspective. Or think of two friends (let's say "Anna" and "Kate") who fall for the same person (let's say "Mason"). Anna confesses her crush on Mason to Kate. Mason falls for Kate, asks her out, and they begin a relationship. Anna is hurt by this and stops talking to Kate. Kate is hurt because her friendship with Anna has suffered. Anyone here can be characterized as the protagonist or the antagonist.
To make sure they are realistic, I like to do extensive character worksheets for my antagonists -- what are their goals? What are their skills/talents? What are their shortcomings/vices? What is important to them? Do their goals, personality, ethics logically flow from their biographical data? Are their reasons for doing what they do compelling?
You shouldn't feel like you
need to do villain's POV. If you have an always-present antagonist force, like say, Cerberus, you wouldn't need to do TIM's POV. I mean, if you have an encounter every chapter and some underling reiterates the antagonist's goal, there's no sense in doing an antagonist's perspective scene or chapter. However, if the antagonist is less obvious, perhaps unknown and pulling strings or the like, doing some scenes or chapters in the his/her POV is useful. You don't have to explain everything, but you can foreshadow. Give your readers something to guess at.
When this latter scenario is the case, I'm usually writing in 3rd person limited POV. I tend to write my protagonist(s) very closely in 3rd person limited, but I don't keep that same level of closeness for the villain. For example, my protag may be thinking long-term and making connections to plans, goals, etc. in her scenes after various minor plot points. In the antagonist's scenes, I like a little more distance, e.g., a scene involving a meeting with an underling where the antagonist makes mysterious gestures/expressions/mannerisms that reveal his/her personality and uses cryptic dialogue (since the antagonist knows what/who/where s/he is referring to), leaving the reader guessing. Critical to these scenes/chapters is that
there is some necessary information I am trying to communicate that I can't get across in any other way in the protagonist's POV.
To your last point, I personally would shy away from writing scenes with your protagonists present from the antagonist's perspective for three reasons: 1) It can be jarring for the reader to be disconnected from the protagonist's viewpoint, 2) It can dull suspense (if your readers want the protagonist to succeed, then experiencing from the antagonist's POV will contradict that), and 3) Usually nothing is gained compared to a scene/chapter where the protagonist is off-screen (i.e., there is nothing to communicate to the reader here that must be accomplished via villain's POV). I wouldn't want to risk #1 and #2 when I can just write a scene from the antagonist's POV without the protagonists there -- a meeting, a planning session, etc. -- and try to reveal the information that way.
In sum, I would just make sure there is something worthwhile to show the reader in the antagonist's scenes/chapters. I feel like many I come across (even in books) are poorly done "Mwahaha, I am planning the bad things for the heroes!" scenes that make me just want to skip them. As a reader, when a villain is first introduced, I want to find out something surprising and critical, like who the antagonist actually is, what makes him/her tick, and so on.
Different strokes for different folks, but that's the way I try to go about it.