Spiritual teachings are maybe most helpful when they become an invitation for inquiry, for exploring what is already here, alive in immediate awareness. In this case, teachings become pointing out instructions and a guided inquiry.
Adyashanti is a master of this form of teaching, even if his talks may take the superficial form of just regular talks. And Genpo Roshi, with his Big Mind process, explicitly and more formally makes his talks into a process of inquiry, allowing the talk to be woven from the inquiry of everyone participating.
They can also be helpful if they inspire to practice, although in this case, they often point to something that appears to be somewhere else, and they may use strategies such as fear and hope to inspire practice, and all of this has its own problems.
This is something we find in more devotional traditions, and for instance also sometimes in Tibetan Buddhism.
Teachings can also be basic and practical information, offering suggestions for practice and some maps to help orient and navigate the terrain. These teachings can be very helpful, in the right context and moderate amounts.
If the teachings become overly abstract, they tend to just remain in the realm of ideas and thoughts. And if they are used by the teacher mainly for entertaining him or herself, or worse, for propping up certain beliefs and fixed viewpoints, they may be even less useful. Although they can, if the recipients take it that way, become mirrors for seeing in oneself the tendency to get lost in and intoxicated by the realm of ideas, and for seeing in oneself the way we use beliefs to prop up other beliefs and fixed viewpoints.
Then there are the expressions of what is alive here now, which may inspire others to look for themselves, and also offer some suggestions for how and where to look. These are often accidental or unintentional teachings, but can still be helpful for others.
Poetry, for instance that of Hafiz and Rumi, is an example of these immediate expressions which may also serve as a pointer, reminder or inspiration.
And finally, as these writings, there are accounts of explorations somewhere on the path, which can also be helpful for others for any of the reasons above, and maybe for a sense of being on the path together.