There is just one answer to that question: directors and limiters. Directors and limiters are specific instructions on what a spell should and should not do. Directors tell the spell what to do. Limiters tell the spell what not to do. Directors and limiters are often more important to a magic spell than any other ingredient.
If you want to launch of spell of any magnitude or power you had better write some directors and limiters to tell the spell exactly what to do. Most people think that the power in the spell is in the chant, the candles, or the herbs. Some power may be in those ingredients, but the guidance for the spell starts with directors and limiters. If you think of a magic spell as a rocket then the directors and limiters are the guidance system. When we teach students in Basic Magic to create and launch spells, always start them with practicing directors and limiters.
What could happen to your magic spell if you don't write directors and limiters for it? The spell might bring you exactly what you ask for but in a way that you might hate. One practitioner launched a generic job spell to get her a dream job. The spell worked like a charm. She got a great job with excellent benefits, amazing salary, and plenty of flex time to spend with her family. The only catch, which she discovered a few months into the job, was that she was working for a mob family. Not good.
This practitioner actually had half the equation right when she launched this spell. She had written a list of directors. She specified the exact parameters of the job she wanted. She told the spell what she wanted it to do. She forgot the limiters, the list that tells the spell not to bring jobs that fall outside the law, or cause death or loss of property. Limiters for magic spells sometimes contain the most significant details!
Luckily, the practitioner was able to write another spell, this time with full directors and limiters, to not only safely get her out of the job with the mob, but also get her another job, this time legal. Tip: no matter what kind of magic spell you use, if it has much power at all write directors and limiters for the spell as insurance!
Reference: asatru-religion.blogspot.com