Purely the fun and enjoyment for me. I love history so I see it as a priviledge to safeguard my items from destruction and to save them for future generations to learn from and enjoy. To be able to hold in my hands the items that were actually there and used in those world altering times, that's just a fantastic feeling that gives me the chills sometimes. I never began collecting with the intent to make a profit. And for a little over a year now, I add the "commraderie" to that list of fun and enjoyment. Being able to chat with collectors from around the world, have meaningful conversations and learning new things, I consider that to be the true "profit" of collecting.
I also agree with Mo. Finding items in the "woodwork" so to speak and paying below or far below market value is a thrill. Much more exciting than just using a PayPal account to buy an item from a dealer. I thoroughly enjoy that adventure and it really puts a smile on my face and keeps this a fun hobby.