The clematis family includes a 250+ species with various native origins on nearly every continent. Here in Wisconsin, there are a few cultivars that perform well and are reliable hardy, like Sweet Autumn and Superba Jackman. Mature sizes vary, but in general as a climbing vine, they grow upward and typically on trellises or fences. Mature heights are varied; however, mature spreads are generally unlisted because vines can keep spreading, depending on how you intend to grow the plant.
They can be used in a wide variety of garden and landscape scenarios. They're versatile, and although their habits are typically similar, it usually comes down to flower color that attracts growers. Here are some different ways you can grow them.
Clematis are ranked by 3 groups, depending on which season(s) they bloom and whether they bloom on old or new wood. This helps guide you on how and when to prune them. You prune them because as they mature upwards, stems can become decrepit and produce fewer flowers.
As they mature upwards, the weight of the "canopy" can become too heavy for the supporting structure or lower stems to handle. Pruning back wilted or old stems helps keep the plant open for air circulation and healthy, helping to avoid common issues like fungal stem rot.
Check out this article (with images) from Fine Gardening on Pruning Clematis.