plus archivelog command - wasting space ?

Hi all,

i realize that everytime i run

backup database plus archivelog, all the archivelog from the beginning of time will also be backup.

i also done some test as in

1) backup database plus archivelog

2) shutdown database normal to force all data to be written to disk

3) startup database again

4) backup database plus archivelog

seems to be the archivelog backed up in step 1 is again backup in step 4.

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q1) is it true that RMAN does not know about what are the exact relevant archivelogs to backup when issue plus archivelog command ?

relevant archivelog = data already written to disk and will be in backup