Some of the benefits of a C&R:
You can buy regulated firearms from other states; no hassles or fees with a local FFL holder, no sales tax.
You can import firearms from other countries; this is rather more complex.
While you must keep records of the firearms you buy or sell using your license, you do not have to turn in the records, and should you decide to not renew your C&R, you can just trash the records. This may be useful if you're concerned about the government knowing what you have.
You get discounts from some wholesalers because you have an FFL license.
You get your guns delivered to your door.
You can only use your license for weapons that are considered curios and relics; they have to be fifty years old or more, or on a list of C&R weapons published by BATFE.
You have to pay 30 dollars every three years.
You will spend a lot of money on guns you never knew you needed.
It's a nice thing to have, especially if you like older guns. I do. I can't really think of a reason to get such a license, if you have any interest in the sort of firearms it applies to.