if it is brass case or nickel plated and not berdan primed, you can reload it. if the case has cracks, major dents that do not come out in resizing, if the flash hole is eroded, if there is a bulge,or corrosion (not dirt or carbon), pitch it. other than that, if it looks good, keep reloading it. depending on caliber you can reload the same brass many times. i just dump it all in a 5 gallon bucket so i dont keep track of how many times it has beed loaded. as you read the ABC's, it will tell you what to look for in inspecting brass.
I only reload pistol rounds, rife is a different story.