It is not necessary.

You can draw anything without any manual compositional planning whatsoever! However...

Freehand Drawing is HARD.

If you can sit back comfortably, keeping your whole panel in view during the drawing process, have an excellent eye and a highly practiced hand, have a lot of talent and experience, and just a little luck, you can avoid mistakes. (Or at least cover up the little ones) This is not easy, requiring decades of practice to be done consistently. There are also really only two reasons to practice this skill: performance art, and ink drawing.

In a final product, nobody can tell whether you drew it freehand or used guidelines to construct your composition. (Except for crazy art lovers, but many of those people actively want to see traces of the construction in the finished work) As such, the only reason you would want to do freehand a drawing with dry media, is if someone is watching you draw it and you want to be committing every mark to a final product. Freehanding can be very impressive to watch, and can earn good tips. As such, it's pretty much only used by street artists, like caricaturists.

Meanwhile, when working with ink, (and some other permanent media, like metalpoint) it can be detrimental to the finished product to use guidelines. Ink does not stick to graphite well. Colored inks will mix with charcoal. Anything between an ink and the paper can cause it to fail to bind correctly, and even make localized changes in bleed. Careless guidelining can damage the paper's tooth, affecting the appearance of the ink mark. Erasers ruin the altered surface. Some inks include a lacquer in their binder, which traps your guidelines and exposes them forever. If you're working in brushed ink, particularly in an eastern calligraphy tradition, the idea of guidelines goes against the very philosophy of the art form. There are ways around these issues, but they require intimate understanding of the physical properties of your media and paper, and result in serious restrictions on material selection. In these media, technical mastery depends on one learning to freehand with a permanent mark.

It is not necessary.

You can draw anything without any manual compositional planning whatsoever! However...

Freehand Drawing is HARD.

If you can sit back comfortably, keeping your whole panel in view during the drawing process, have an excellent eye and a highly practiced hand, have a lot of talent and experience, and just a little luck, you can avoid mistakes. (Or at least cover up the little ones) This is not easy, requiring decades of practice to be done consistently. Thus, it is far more practical to first manually plan one's composition using guidelines, contour lines, line of action, perspective, and other forms of composition construction lines. It bypasses the demand of practicing freehand for 15+ years, allowing the artist to become technically competent within weeks of dedicated practice, ensuring consistent results. There are also really only two reasons to practice freehand drawing: performance art, and ink drawing.

In a final product, nobody can tell whether you drew it freehand or used guidelines to construct your composition. (Except for crazy art lovers, but many of those people actively want to see traces of the construction in the finished work) As such, the only reason you would want to do freehand a drawing with dry media, is if someone is watching you draw it and you want to be committing every mark to a final product. Freehanding can be very impressive to watch, and can earn good tips. As such, it's pretty much only used by street artists, like caricaturists.

Meanwhile, when working with ink, (and some other permanent media, like metalpoint) it can be detrimental to the finished product to use guidelines. Ink does not stick to graphite well. Colored inks will mix with charcoal. Anything between an ink and the paper can cause it to fail to bind correctly, and even make localized changes in bleed. Careless guidelining can damage the paper's tooth, affecting the appearance of the ink mark. Erasers ruin the altered surface. Some inks include a lacquer in their binder, which traps your guidelines and exposes them forever. If you're working in brushed ink, particularly in an eastern calligraphy tradition, the idea of guidelines goes against the very philosophy of the art form. There are ways around these issues, but they require intimate understanding of the physical properties of your media and paper, and result in serious restrictions on material selection. In these media, technical mastery depends on one learning to freehand with a permanent mark.