* The owner's preference: Some owners prefer a neat and tidy look and will trim or braid their horse's mane. Others prefer the natural look and leave the mane long.
* The horse's purpose: Show horses often have their manes braided or clipped for a polished appearance.
* Practical considerations: Long manes can be prone to tangling and mats, especially for horses living in humid or muddy conditions. Trimming can help with this.
So, the answer is that it depends on the owner and the specific circumstances.