Research about homework (of any kind, not just for sound production) has demonstrated that its purpose is to take an already strong skill and make it more automatic. Therefore, whatever we send home should be something that a student can do easily. Often, that will mean that home practice is one or two steps behind what is targeted in treatment. For example, a student may have already progressed from pre-practice (mastering the sound in isolation or syllables with 80% accuracy or great) to practice (wherein we mix the practice across various levels - syllables, words, phrases, sentences, conversation - and while varying other elements - actions, emotions, activities, etc.). If the child still needs some support in the practice phase, sending home something at the pre-practice phase will often be appropriate. For example, if a child is working on /s/ in the practice phase, home practice may consist of saying /s/ in isolation or syllables (a skill he or she has already mastered).
For children who have already established sounds, these home practice sheets to offer opportunities for further automaticity. Many SLPs are familiar with the wonderful Iowa phonetics website. The homework sheets show families step by step how to utilize this website for practicing each fricative, affricate, liquid and the stops /k/ and /g/ in isolation. This has worked well for many students last year and has provided motivation because of interest in technology.