Hrm…
Nothing really “eats up” points. Basically, whatever you juggle with adds points to an invisible juggle counter with a pre-determined value, and if you want to keep juggling, you have to hit with a move that has a juggle potential value that is higher than the value currently in the juggle counter (to put it simply).
So, since each hit of spiral rocky has a juggle potential of 4, as long as the juggle counter is at 3 or less, it will juggle.
The reason each hit of spiral rocky connects is because they don’t add to the juggle counter. If the juggle counter is at 3, the first hit of spiral rocky will connect (it has a potential of 4), and it doesn’t add any points to the counter, so the counter stays at 3. This lets the next hit of spiral rocky connect, and so on.
The last hit of spiral rocky adds 4 points to the counter. So now you can only juggle with a move that has a juggle potential value higher than the number currently in the juggle counter (at least 4 or more).
Poundcake has a juggle value of 6, Cracker Jacker has a juggle value of 10, and Giga Jacker has a juggle value of 6. These are the only moves AFAIK that have a juggle potential higher than 4… and Giga Jacker is the only move that you can realistically connect with after spiral rocky (due to obvious reasons).
As for tag cancelling… that’s a different beast altogether I think. In practice (and I’m not 100% sure on how it works) when you switch cancel, you reset the juggle counter down to 0, for BOTH characters. The character you switched from now gets reset counter, AND the character that runs onscreen gets a 0 counter. There are exceptions (Ryu shinsho for example) but that seems to be the general rule?
There are a few extra things to note as well. When an attack is the initial knockdown in the combo, and it’s a natural knockdown, it generally doesn’t add anything to the juggle counter. There are a few exceptions throughout the game (due to balancing from Capcom I guess?) but if, for example, you anti-air with a cracker, the juggle counter will be at 0 when you continue your combo even though a cracker normally adds 3 points to the juggle counter when used in a combo. But if you cause an initial knockdown with an attack that ISN’T a natural knockdown attack (a counter-hit jump attack for example), it will add to the juggle counter regardless.
Overall it sounds quite complicated, but once you get the hang of it, and learn the juggle values of the moves, it will all make perfect sense. For the raw data, you can find it here: http://pandora.dantarion.com/dumps/BOB.bac.scripts.html It’s daunting I know, but it’s all there, just add 1 to each column 13, and collumn 14 is how much it adds to the counter (the +1 addition is weird I know, but this value system is probably best for practical discussion)
What is really interesting though, is that Bob has A LOT of moves that don’t add to the juggle counter! I can think of 10 off the top of my head (the 2nd hit in all 4 of his tekken-strings, poundcake, cracker jacker, apres sweep, double chapati, and EX/regular spinner ball). Theoretically, if you could connect with only these attacks, the juggle counter would never increase, and you could juggle with them infinitely! EX Spinner roll is one easy example… with infinite meter, you can do this move infinitely because it never adds to the juggle counter, allowing you to keep juggling with it forever. Try it in training mode! 