Just that they have been there a long time and there is more of a chance that the tooth could be cracked or become decayed and need to be pulled because another root canal may not be able to save it?

A tooth that has had a crown placed is more likely to require root canal at some point. Dental crowns are usually used to rebuild teeth that have experienced some type of significant structural damage. And as it happens, these same types of events can also insult or compromise the tooth’s nerve tissue and therefore create a need for root canal treatment too.