Taking a pause is always wise, because both the body and any intestninal flora effected by the herbs will adapt to the treatment. Often there's a lowering of effect because of that adaptation.
In short, it's to prevent a dependency, where dosages would need to be ramped up to achieve the same results.
Also, it gives the body a chance to take over the immune-system boosting qualities after the removal of the herbs. Goldenseal is, for example, nicely antiviral, so it's a good idea to give the body time to realise it can continue fighting any infections present on it's own and create the needed antibodies and store the data.
Personally I'd say give it two weeks and take up the herbs again if the symptoms that you were originally treating show up again.
Herbs are also nutrition alongside medicinal. It's important your system isn't oversaturated for too long with only one profile of nutrients, because that can create a lean towards deficiencies in other nutrients. For example, coffee (a traditional deworming herb) is rich in many minerals, folate and salicylic acid (aka vitamin B11), but prolonged intake of vitamin B11 without vitamin B12 will make the liver's stores of B12 drop.
B12 is part of the methylation/glutathione cycle and creating energy, so the coffee drinker can feel a clear difference after drinking coffee-- the caffine and folate provide a temporary boost, but can't provide the B12 (cobalt).