IK Is Not Always OK.
One thing I've noticed a lot of students do recently is animate with IK on for no apparent reason. For example, a character just walking forward in space and gesturing with his/her arms would be animated with the arms in IK. I'm not sure if this is a rookie mistake, laziness, or if people do it so they don't have to deal with orientation switches but, in my opinion it is very noticeable and it almost always looks wrong. If we just look at the terminology we're using we can get some obvious hints that will help you with your work method. "Inverse" means the reverse of something. So the opposite of FK, or forward motion, must be obstructed motion or motion impacted by an external element.
That external element makes perfect sense when it's something like a ground plane, table top, or any surface that your character may need to interact with. However, if a character is just walking around or standing still and gesturing and the arms are free of any external element, then IK stands out like a sore thumb and your animation looks like a puppet with arm rods. Movement begins to look externally motivated. You don't want to do anything that's going to break your "illusion of life". I love the Muppets as much as the next guy and those characters seem real to many people but Kermit's arms still look like their on sticks..... which is just bad IK.