Goodness, I can think of a whole lot of reasons why I prefer a church structure to a home church......
1) It allows for more growth (and after all, isn't that what we are supposed to do-bring people into the fellowship of believers?!)
2) Since the church can be larger, it allows more opportunity for people to connect with one another and on many different levels. For example, in my church there might be an older lady who I have developed a relationship with and when I need someone to mentor me, she might be who I would talk with. At the same time, because we are large enough to allow it, there might be a younger woman who looks to me when she needs someone to mentor her.
3) Sometimes I have something going on in my life that I don't want the whole church to know about, but want to go to an altar to spend time in prayer. In a small group of only 10-20 people, it is much more likely that everyone is going to know each other on a MUCH more intimate level and so, instead of being to go to God to seek HIS answers, people will tend to want to give advice to one another even if you have not sought out that advice
4) A larger church would allow for many more different opportunities for ministry. It might not be my gift to do music, but it is someone else's. But my gift might be organizing a free clothing give-away to reach out to the needy. That might not be your gift, but your gift might be teaching,..... you get the picture.
5) I wanted my kids involved in a strong support group thru church when they were in school so that when they ran up against something tempting them, they could lean on their friends in the school building to help support them. In a small group, you might only have one or two youth. That's not alot of support.
That's 5 of the reasons I like the church building and prefer a church of at least 60-100 people. There are many more reasons.
But having said that, I also have to tell you that one of the things I really love at our church are the small groups. We come together on Sunday mornings as a whole. And we all do different ministries as a whole (missions work both local and foreign, youth activities, etc.). But we also have some very powerful small groups that meet weekly. Our Tuesday Ladies' Bible Study is one of them. We have about 15 of us and we are a very tightly knit group, but we are always open to new people joining us. In fact, we just had 4 or 5 more join us 2 weeks ago when we started our newest study on the book of Nehemiah

Tuesday is my favorite night of the week