Sure, you can leave cushions outdoors when using outdoor furniture, but again with some measured caution. The general rule is that most outdoor cushions, much like those in the Ovios BBR Broad Armrests Series, are fabricated for water resistance and quick drying. However, they are not wholly waterproof.
Cushions can be left outside for everyday use; they will generally be able to handle minor rain or morning dew. However, when heavier rain sets in, it is a good idea to take them inside or to cover them up. This will help prevent water from seeping into the filling of the cushion and creating mold and mildew.
If it is winter or if you're not going to use the furniture in a long time, you can store the cushions indoors. This will protect the cushions from the weather and prolong their life. An available garage, a shed, or even a storage box big enough serves well.
If you don't have storage indoors for the furniture, consider waterproof furniture covers. These protect both the furniture and the cushions from rain and sun damage.
Even cushions that are weather-resistant will last longer with a little TLC. Protect them from the worst of the weather, and your outdoor seating areas will be comfortable and beautiful for years to come.