If you only want to process content updates from the SMB (documents which are added, modified, or removed), then click on Incremental instead of Full.
The SMB connector will automatically identify only changes which have occurred since the last crawl.
If this is the first time that the connector has crawled, the action of the "Incremental" button depends on the exact method of change discovery.
It may perform the same action as a Full crawl crawling everything, or it may not crawl anything.
Thereafter, the Incremental button will only crawl updates.