Starting note: cap iron = chipbreaker.
For example, moving the frog back is for taking larger shavings and less figured wood. Moving it up is for smaller shavings and more figured woods.
A similar logic applies with the chip breaker.
That's correct in essence but you can simplify matters for yourself greatly if you take the frog out of the equation.
You can set the frog back so that it lines up with the mouth, giving full support for the iron along its length and down to as near to the cutting edge as the design of these planes allows. You can then leave the frog there for extended periods, permanently if you like. Some users never move the frog on a Bailey-style plane and there's a good reason they can get away with it.
The reason is you can control tearout effectively using the cap iron/chipbreaker alone1.
The cap iron is often used in concert with shaving thickness to conquer tearout but it's so effective it is possible to get tearout-free performance without having to take very very thin "lacy" or "feathery" shavings. Ultra-thin shavings can by themselves give very good results WRT tearout, but using the cap iron you can take heavier shavings and get the same (or better) results2.
Would you ever use the chip breaker really opened up but with a tight mouth?
Yes you would. In fact you'd often need to because the combination of a close cap iron and a tight mouth will often lead to shavings that clog the mouth almost immediately.
So if you move the frog forward you generally will need to back off the cap iron somewhat. You can tweak things on some planes so that you can have a close (or close-ish) cap iron and a tight mouth, but you'll probably find that this is not really worth messing about with since the cap-iron setting by itself can do all you need.
The setting for the cap iron could be thought of as: as far back as possible, as close as needed. But you'd probably appreciate some numbers as we all did when we were starting out so...
Setting the cap iron, some numbers
For a no. 4 set up as a smoothing plane you'll rarely, if ever, want to set the cap iron more than 1/16" away from the cutting edge. Basically there are no situations where you'll want/feel the need to have it set further back than this as the plane won't be called upon to take shavings heavy enough to warrant it.
Similar settings can be used for nos. 6, 7 and 8, and for a no. 5 if it isn't set up in the traditional manner for heavier material removal (5s can be used as longer smoother planes instead, or short jointers or fore planes).
For a jack plane used in the traditional way (with a fairly obvious radius on the cutting edge) or any Bailey-pattern plane converted to scrub or roughing use (even more pronounced radius on the cutting edge) you can set the cap iron as far back as the plane will allow. In practice this will be 1/4" (6mm)or a little more (note that once the cap iron is a certain distance back you don't gain any benefit from moving it away any more, and many planes won't allow a setting much greater than this anyway because of the distance between the cutting edge and the slot that the Y-shaped lever goes into).
So a quick summary, approximate settings for the cap iron/chipbreaker for various tasks:
- 1/4" (6mm) back for rough work (jack plane hogging off wood)
- 1/8" (3mm) back for long-grain shavings in easy wood
- 1/16" (1.5mm) for wood that has some tendency to tear out, could be thought of as the default setting for a smoother
- 1/64" or closer (under 0.4mm) for any very challenging planing — lots of knots, burr woods, interlocked grain/reversing grain, and for planing against the grain when there's no choice (e.g. when planing a lamination where all the boards couldn't be aligned to the same grain direction)
Note: don't get into the habit of trying to measure these distances, apart from not being efficient it's not possible once you get to the finest settings. Instead learn to eyeball it, you'll soon get the knack and it only needs to be approximately .
1 This is the reason it was developed.
2 This obviously increases productivity and it's why double-iron planes very quickly came to dominate smooth-plane manufacture and purchasing, pushing single-iron bench planes nearly out of existence.