Depth Of Field

A telephoto lens, especially the zoom variety, have distinct issues with depth of field issues. That is the part of the image that is in focus at any time. This can be used to great advantage, For example to focus on something, like a flower at close range, and push a distracting background out of focus. Some telephoto zooms have a macro setting or switch for such closeups.

Alternatively, a foreground object can be used to “frame” an interesting subject in the background.

The obvious disadvantage is you can’t have both in focus at the same time.