This is an excellent question and the short answer you’ll be happy to hear is YES! Trail running is used by many road running enthusiasts both amateur and professional for their long run as it is easier on the body. Because trails are generally softer terrain than concrete or bitumen there are less impact forces exerted on your body. This means that you can run longer on this kind of terrain and not have to absorb quite as much impact forces over all.
Trail running also promotes the development of many of the finer control muscles to develop balance and coordination while running. This is excellent if you want to compete in road racing or cross country events that are likely to be less technical than outright trails in the bush. No matter whether it is single track or fire-trail you’ll still find yourself dodging rocks and roots which means you’re incorporating lateral movements into your training.
Hills are an excellent benefit of trail running as well, usually where there’s trails, there’s hills in my experience. Having plenty of hills in your long run is a great way to make it both challenging and scenic which are both bonuses when you’re running for a few hours. There are so many options for hills but on your long run just getting to the top with a reasonable heart rate is fine, you don’t need to get to the top as fast as you can.
Tempo running on fire trails or cross country style courses is a great way to learn how to maximise speed and manage change of pace during a hard run. When trying to run fast on uneven terrain there are sections where you can run fast and sections where you just cannot. To get the best time you have to learn to know when to speed up and slow down. This is particularly important for cross country and for shorter trail running races.
If you’ve never been trail running before it’s definitely best to take someone with you, particularly if you’re planning on doing a long run. Additionally if you’re uninitiated and the trail is going to be rocky, it is worth noting that you may need some proper trail running shoes to protect your feet from pointy rocks and sharp sticks. For extra long runs (15km+) you’ll also likely want to carry some water either in a belt, hand bottle or hydration pack.