This dialog combines the following commands: Protect archive, creating recovery volumes, Lock archive. All they are supported only by RAR archive format.
Protecting an archive may help to repair it later in case of small physical damage of the archive data. If you wish to protect an archive from damage, you need to specify a size of the recovery record in percent to the total archive size. Maximum allowed value is 100%. If you set this field to 0, the recovery record will not be added. Larger recovery record allows to recover from more serious damages, but at the same time it increases archive size, so 3 - 5% is probably optimal.
The special case of archive protecting is generating recovery volumes. It is possible only if an opened archive is the first file in the multivolume sequence, in this case you just need to select the number of .rev files to create. You may also append a percent character to this parameter, in such case the number of creating .rev files will be equal to this percent taken from the total number of RAR volumes. Each recovery volume allows to reconstruct one missing volume file. You may read more about this feature here.
Set "Disable archive modifications" option if you wish to lock an important archive, so WinRAR cannot modify it. Locking important archives prevents their accidental modification by WinRAR. This option is not intended or able to prevent modification by other tools or willful third party. It implements a safety measure only for accidental data change by WinRAR.
Recovery volumes has a higher precedence than other options and cannot be combined with them. If you specified non-zero number of .rev files, WinRAR will ignore recovery record and archive lock parameters and will create recovery volumes.