Each form that a formula takes -- oil, incense, powder, bath crystals -- is suited to a different method of deployment. More details here:Sapphyre wrote: [For example,] Does Love me prefer to be used as an oil? Does Banishing prefer to be used as a powder? Or do these decisions tend to be made according to the individual circumstance, or combination of workings within a working?
Now, to return to your questions about these two particular products:
Both of them are available as bath crystals because cleansing and purifying is not the only reason to bathe, and there are other things you can do with bathwater after you have bathed.
Water from a Love Me bath could be fed to your intended. Water from a Banishing bath could be used to spike your target's cleaning supplies to clean them right out of their house.
They are both available as oils because oils are useful for dressing candles; and anointing (of people) can be done for both positive and negative purposes.
They are available as powders to dust objects that would be stained by oil, to keep your work inobtrusive -- or, more traditionally, sprinkled where your target will walk, either to lead them to you in love or to send them out of your life.
They are available as incenses because the smoke of incense is an offering to God, carries prayer upward and outward, and repels all kinds of evil. (Also, if you don't have a varied collection of herbs, you can sprinkle a pinch of incense powder on a candle.)
In my experience, the form you choose depends largely on the opportunities you have.
You can also mix and match formulas to fine-tune your work. I generally mix King Solomon Wisdom into love work, for instance. I don't always just blend the two oils, though you can certainly do that; sometimes I use them alternately, or put a drop of King Solomon Wisdom Oil on a little mound of love incense, or the other way 'round -- just for starters.
When each formula comes in four different forms, the possibilities for your workings are multiplied many times over.