Ok, a very specific answer to your specific question is after the torrent reaches 100% complete, you’re then a “seeder”, and the files will continue to upload.
On BitComet, look at your “ratio” column (if its not present, “right click” on any column header and select it from the list of optional columns). A ratio above 1.000 means you’ve uploaded more then you’ve downloaded, if it is less, then you should continue the task until it uploads more.
After your task has reached an acceptable ratio and is stopped, it will remain available for LTseeding. This is a downloading protocol unique to bitcomet and the files can be shared with other bitcomet users if you have the LTseed option enabled and your bandwidth isn’t in demand by other tasks.
When a task is both stopped and removed from bitcomet, then it will no longer be shared in any way.
This is just one additional way that bitcomet helps you to share the files you have downloaded. You should also note that enabling LTseed can greatly increase your download performance.