Felt the need to share given my unique perspective on fraternity life. Full disclosure, I'm a rising senior and a member of one of the larger fraternities on campus. First, I will say that when people say that fraternities aren't for everyone they are absolutely correct, but there is a large group of people that join houses and really flourish.
Both of my parents went to ISU and didn't do the Greek thing, so when I went to school I followed the same path. Lived in the dorms my freshman year with a high school friend (sophomore) and had a good experience. Looked at Greek life a little bit, but was a little wary of how big of a commitment it was. Became a CA/RA during my sophomore year, thus lived alone. At the time I was a part of an organization that was primarilty composed of Greek students and found that I really enjoyed spending time with them (in a non-partying setting). In addition, since I was a CA for about 70 co-ed students, I was finding it hard to interact with my peers in a social setting. Both of those factors combined led me to pledge my house, which has a been a great experience. I lived in the house my junior year and will be in an apartment with three of my "brothers" this year.
Pros to Fraternity Life: Automatic network, like many have referenced, once you join you are automatically connected to thousands of people across the country. I'm pursuing a job that doesn't recruit at ISU and having a network of brothers at different universities across the country was a huge help in landing my internship. High standards, this didn't apply to me because I set high expectations for myself, but if you're someone who struggles with motivations a fraternity does have academic, service, and involvement standards that "force" you to do your best in college. Social, great way to meet both guys and girls. Competition, if you like competition Greek Week and Homecoming are great ways to compete against other houses on campus. There's more but you can PM if you want to know more.
Cons: If you're not ready for it, the time commitment can be burdensome. Some people struggle to balance all of it while maintaining good grades. Living in a house with 50 guys can get a little gross, as I'm sure most can imagine.
In the end, it's all about what your son wants. If you're not ready for it, he'll be miserable, but at the same time, you don't want to regret not giving it a shot. My advice would be to live in the dorms for a semester and do a little research on the house he wants to join, try to hang out with some of the guys so you keep good ties, then you can make his decision on his terms.
Just to add, depending on the house the costs can actually be cheaper to live in the fraternity. Also, August 1st is the deadline so they know how many guys they have living in the house and can set their budget (I was the treasurer for my house last year). It sounds like your son was contacted late in the process, typically kids are recruited for the whole summer, including events, before they have to make a decision.
Feel free to PM me, would be happy to chat over the phone with your son about the options.