1. You can do a lot of things in a mediocre (or poor) way, or you can do a few things extremely well. Craig Groeschel has some great things to say about this subject. Also check out Thom Rainer and Eric Geiger's Simple Church.
2. Over-programming creates an illusion of fruitfulness that may just be busy-ness. A bustling crowd may not be spiritually changed or engaged in mission at all. And as our flesh cries out for works, many times filling our programs with eager, even servant-minded people is a way to appeal to self-righteousness.
3. Over-programming is a detriment to single-mindedness in a community. If we're all busy engaging our interests in and pursuits of different things, we will have a harder time enjoying the "one accord" prescribed by the New Testament.
4. Over-programming runs the risk of turning a church into a host of extracurricular activities, mirroring the "Type-A family" mode of suburban achievers. The church can become a grocery store or more spiritual YMCA, then, perfect for people who want religious activities on their calendar.
5. Over-programming dilutes actual ministry effectiveness. Because it can overextend leaders, increase administration, tax the time of church members, and sap financial and material resources from churches.
6. Over-programming leads to segmentation among ages, life stages, and affinities, which can create divisions in a church body.
7. Over-programming creates satisfaction in an illusion of success; meanwhile mission suffers.
8. Over-programming reduces margin in the lives of church members.
9. Over-programming gets a church further away from the New Testament vision of the local church.
10. Over-programming is usually the result of lack of reflective "reflex reactions" to perceived needs and and an inability to kill sacred cows that are actually already dead.
(Read the full post over at The Gospel-Driven Church)