Their maximum length is usually 135 cm (54 inches), however, unlike ski poles, they are often made in two or three sections and can be extended and retracted as necessary for use and collapsed for storage or transport.
They can also be used as aids when climbing rocks or boulders, to probe the depth of mud or water and facilitate a crossing.
In particular, the most common complaint is that the carbide tips leave visible white scratches on rock and make scraping sounds.
[1] The Appalachian Trail Conservancy (ATC) recommends several measures to mitigate the environmental impact of trekking poles in accordance with Leave No Trace principles of low-impact backcountry recreation.
On level sections, or in areas where the potential for adverse impact is high, the ATC suggests putting the poles away entirely.