It's easier to delete a STAR and enter a Direct To leg or Heading, rather than entering a STAR at the last minute. In many places the STAR will also give you a good idea of expected altitude restrictions, making VNAV predictions easier. Also, in the event of an FMC failure, you will have it in the CDU as a backup.
If the weather is such that you can't readily predict the runway, plan for the closest one (shortest ground track). If it turns out to be a different one, you have more time to change and brief.