A Lot of time students ask if they should use Inverse kinematics or Forward kinematics on things like arms. It all has to do with the shot and what is going on. Lets say a character is leaning on a desk, then gestures and picks up a cup of coffee and drinks it. it makes sense to use inverse kinematics until his hand leaves the desk, then switch to FK for the gesture and picking the cup and drinking it. But this is not the only way to do it. Ultimately it will come down to making it look natural. We want to avoid the look of a puppet on strings. Sometimes IK on arms can cause this look. That is why the gesture is animated using FK. When the arm is on the table it makes sense to have the joint solved by IK. It would be a compositional nightmare to do it another way. Being able to control the pick up of the cup and putting it to the mouth is up for debate about when and if IK is really necessary. If you can pull it off with FK, then it is a good approach. Its important to keep things as simple as possible. Turning on and off IK can be difficult especially if you have to change the scene. Another thing to take into consideration is when to use arm alignment. Basically, arm align gives you a bit more control over the patterns of your acting. If you rotate the characters root, the arms will not be as affected by that rotation. It gives you a bit more control, especially for acting shots. I usually have this on. It tends to make the character look a bit more organic but can also cause a bit of a head ache if you are doing alot of rotations with the characters body.
I used to know an animator who animated all his gestures using IK. I never understood how he did it. The point is that people will use what they feel comfortable with. There is no one way, but you can save yourself a lot of headaches if you use the right tool for the right project. I’d love to know how people work and what has worked for them.