How to increase weight on weight bar exercises?

On exercises using the weighted bars, how should we be increasing weight? 

For instance, I just Mastered HS/PE4 using a weighted bar @ 10lbs. I'm assuming I should move on to HS/PE5 and continue to practice HS/PE4 with a 15lbs bar as a warm up?

Would there ever be a case where you wouldn't want to keep increasing weight? 

See this post from the course wiki. As far as volume goes, I find 2-4 work sets is usually reasonable, depending on how fast I want to improve and whether the movement will interfere with anything I'm doing in my main workout. 

Joshua Slocum said:

This is intended as a guide for how to safely increase weight and/or ROM on mobility exercises where progressing too far too quickly can pose a risk. Examples include inside squats, Jefferson curls, and weighted dislocates (not a complete list).
 
Figuring out where to start
First, you need to figure out what ROM/weight to start out with. This is a fairly simple process. Pick an intensity that you think should be easy for you. Now go two steps easier than that, and try performing the exercise that way. If it's easy for you to perform the exercise correctly, increase the intensity by a half a step and try again. Keep increasing the intensity until you find a level where performing the exercise is a challenge, but you're still able to maintain correct form. This is the level you should be working at. 
 
If there is any pain, you're using too much intensity. [Note the difference between pain and discomfort]
 
When to increase
Coach has two good posts on this subject - it's worth reading them:
https://www.gymnasticbodies.com/forum/topic/18263-jefferson-curl/?p=175032
https://www.gymnasticbodies.com/forum/topic/18263-jefferson-curl/?p=175063
 
You want your exercise to go through three phases: overload, just load, and underload. In overload, the exercise is a significant challenge. In load (or 'just load'), the exercise will be effortful but not too much so. In underload, the exercise is easy. The underload period is where your body 'locks in' the new weight/ROM. Optimum underload periods will depend on the individual, but usually will be a few weeks. 
 
 
How much to increase
After your underload period, you're ready to increase the weight/ROM again. You'll want to use essentially the same procedure you used when you were figuring out where to start. Begin by performing the movement with slightly more intensity than you currently use. If that's still easy, continue adding intensity and trying the movement. Keep going until you again find an intensity that is challenging but doable. 
 
Intensity increases can sometimes be quite dramatic - a 50% weight increase is high but not unheard of. The right increase can also vary from person to person and from cycle to cycle, which is why it's important to reassess the right intensity after each underload period.