Hello,
many thanks.
If you de-select files, they are not normally deleted from the destination. Such a deletion would only happen if you use Exact Mirror mode and click the Configure button and choose "Remove Deselected Subfolders and Files From Destination".
2. What is the fate of new files/directories created after a backup ? Do the new files/directory are included by default ?
New files and directories are only included by default if they are in a folder which is completely selected. If you deselect some files in a folder, then new files in that folder are not selected. But new files in other folders are added automatically, if those folders do not have a file level selection.
For this reason, I usually recommend Exclusion Masks.
If you add items to the Exclusiom Masks in the profile, these will only affect the profile. The Global Exclusion Masks are on the Program Settings dialog. Those affect all profiles (unless you disable them in a profile).