A patch lube should be found that provides the best consistency with the powder and load that's being fired, whether at the range or in the field.
To switch around the patch lubes doesn't make much sense because that's altering the load and possibly its performance.
And spit is only really used much by those loading with real black powder and not with the sub powders.
There are much better lubes than spit. Spit is only used because it's better than using nothing when loading a ball down a barrel that's fouled with black powder residue.
A good lube should help to keep the barrel clean by effectively swabbing the barrel during the process of ramming each subsequent PRB.
It helps to soften the fouling so that it can be partially pushed down into the breech during ramming.
That allows many more shots to be fired in a row without needing to swab the barrel as frequently in between shots.
The frequency of swabbing is determined by the amount of powder loaded and the resulting accuracy. The more powder that's loaded the more fouling that's produced. Loading more powder often leads to needing a more effective patch lube than spit to continue shooting without more frequent swabbing.
Swabbing some barrels clean can sometimes hurt accuracy as much as having too much fouling.
Every gun barrel and loading are different and so is each patch lube.
If the right patch lube is used the amount of fouling in the barrel stays pretty consistent for a lot more shots and so will the performance.