Well, the latter question is easy to answer. Every creature (yes, including bugs) needs a place to live. Sometimes, bugs make your plants their home. Most people welcome butterflies and lady bugs as "acceptable" bugs - yes, they are bugs - even though they're "cute"! Other bugs, such as beetles, wasps, and spiders, are not so welcome by most people.
Often, bugs aggregate on plants because the plant is a source of food. In some cases, such as Monarch caterpillars feeding on Milkweed, we welcome the bugs (a butterfly has to come from somewhere). But in most cases, we consider such bugs pest in the landscape.
At EPLS, we consider your landscape plants, pests, and presence of beneficial insects as part of our treatment program. We even collaborate with researches at the University of Florida to identify new pest introductions and monitor resistance in pest populations!