Prefixes and suffixes set in the Feed settings, appear in the post originating from that feed no matter where it ends up going (Twitter, Facebook, LinkedIn, etc.)
Example: You may indicate the source of a post i.e "New Blog Post-"
Prefixes and suffixes set in the Social settings are only sent to that destination.
Example: You may want to include something specific to that account like "Twitter Tuesday".
If you include both source and destination prefixes and suffixes, they're displayed on the resulting posts like this:
[Destination Prefix] [Source Prefix] [Item Content - Title/Body/Url] [Source Suffix] [Destination Suffix]
Please note that in any of these prefix or suffix fields, there is a character limit of 20 characters.
You can use source and destination prefixes/suffixes in a single route. If you were to use all four fields in a single route the output would be:
[Destination Prefix] [Source Prefix] Headline Body URL [Source Suffix] [Destination Suffix]
If used, the destination prefix/suffix will always appear at the very beginning and very end of the output string -- effectively wrapping the rest of the content.
This approach provides a tremendous amount of flexibility and control over prefixes/suffixes. Post away!