It specifies whether avast! "enters" the reparse points on the filesystem during scan.
For example, the folder C:\Documents and Settings on Windows Vista and higher is actually not a folder - but rather a link to C:\Users. If this option is activated, avast! will scan the content of the link target (i.e. C:\Users) when it arrives at C:\Documents and Settings. If the option is disabled, it will ignore this "folder" and simply go on with the next one.
Except for special cases (multi-OS setup, hard disk with another OS attached to your computer), I suggest to keep this setting enabled - avast! has special logic to prevent multiple scanning of the same area (so in the example mentioned above, if you're scannig the whole C: drive, avast! would actually skip scanning C:\Documents and Settings anyway, because it knows that it arrives to C:\Users sooner or later; the difference would be in case if you were scanning the folder C:\Documents and Settings alone, or this and a few additional folders).
