If you add raw ground beef, what about the grease in the meat mixing in with the chili? ill..
The amount of grease the meat exudes is dependent upon the amount of fat in the beef. If your beef is lean (<10% fat), you will not likely notice a difference in the greasiness in the final product by not straining. If your meat is fatty (ground beef in the US can contain up to 30% fat), then the final product will have noticeable grease. The fat contributes in a good way (IMO) to the flavor and mouth-feel of chili if the meat is in the 15% range.