SB is an incredibly powerful tool. A tool that I've just recently started to FULLY realize the power of.
There is NO reason to remove duplicate domains. The original reason to remove duplicate domains was because SB used to automatically alphabetize the URLs (that is, sort them alphabetically).
This meant that you'd be commenting on the same domain right in succession.
NOTHING looks more like spam to a blog owner than getting somebody who has commented (with their comments all linking back to one site) on their blog 50 times in 10 seconds...which is exactly what happens when you're commenting on a list of blogs without duplicate domains removed alphabetically.
HOWEVER, now that SB has the feature to randomize your list of blogs on import (open up settings & check the last option) this doesn't have to happen.
So lets say you have a list of 30k unique domains and a list of 20k urls that are sharing 5k domains. That means you've got 50k unique URLs total coming from a total of 35k domains.
That means you've got roughly 4 urls from one domain for your second list. When randomized into the total 50k list, you won't be commenting on the same blog domain repeatedly. Depending on how far that one domain entry is from the last, it could be a 30 minute span from one comment to the next...which looks fine to a blog owner.
AND GOOGLE WILL COUNT THEM!! If you have a link from one blog URL and another one from another blog URL (sharing the same domain), google will count them, I can assure you.
Why do this? Well, there are a lot of reasons, but I'll name the main two (in my opinion):
Outbound Link Number &
Each Pages PR
One of those URLs you commented on might have 500 outbound links and the other might have 5 outbound links. You get to put yours one both.
One page might have N/A PR & the other might be a pr 4. You get your link on both.
Google counts both links.
Both links will be found.
Both links contribute to the anchor text percentages search engines are calculating for your site.
Don't remove duplicate domains IF your list is sufficiently large to fully scatter & randomize the number of times & the time span in between when you're commenting on the same domains.
I've got 25k backlinks to a site is YSE & 21k backlinks in Google Webmaster Tools...all inside of 1 month using SB and another tool EXCLUSIVELY, and you would seriously not believe how many in BOTH of those (YSE & GWT) are from the same domain but different URLs.
Trust me, it's worth it to comment on different URLs of the same domain. You wouldn't believe my jump in rankings by doing this, particularly by commenting on EVERY indexed URL of every autoapprove blog I could find.
Read this thread:
http://www.blackhatworld.com/blackh...re-comments-approved-backlinks-scrapebox.html