Said at Southern has a nice post on "What's So Great About Seminary." In sum his main points are:
1. It’s a great privilege to be instructed in God’s Word by godly men.
2. It’s one way to become competent in many skills useful in ministry.
3. It’s an opportunity to make lifelong friends who will encourage your ministry.
4. It’s a intense experience that will train you in perseverance, a quality essential for pastors.
5. It’s a safe setting for theological reflection and to confirm the reliability of the scriptures.
6. It forces most students to live in greater dependence upon God.
7. It’s a time to clarify the mode of ministry to which God is calling you.
8. It’s a chance for younger men to gain valuable maturity.
9. It’s a system that screens out many who are unqualified for the ministry.
10. It’s a time that eventually will come to an end.