If you buy a dropped domain from Snap or Namejet, the backlinks seem to be worthless for SEO.  They are valuable for traffic if it's targeted to your site.  Go ahead and 301 redirect into your site because it's the traffic from the back links that is worth something.  I use the Google URL builder to redirect these names so you can see the domain the traffic is coming from.
For example, placing your backorder at NameJet will reveal your interest to other potential buyers so if no other backorders are present you should wait until the last possible moment before the deadline to place your backorder — because if you’re the only backorder, you’ll get it for the minimum $39 bid on expiring names and it won’t go to auction.
Some jerk stole my .com domain name after I had owned it for 10 years and accidentally let it expire, and he’s trying to extort lots of money from me for its return. On the site where it says who owns it, it says “Domain Status: clientTransferProhibited”. What does that mean? The domain expires on September 26. He’ll probably automatically renew it, like he has for the past couple of years. But in case it becomes available, I want to grab it. I’m the only person in the world with my name, and I posted at a blog for 10 years with that domain name. So I’m really upset I don’t have my own name anymore.

To get the most from GoDaddy Auctions, you should first decide on the way you want to evaluate the domains. Domainers tend to look at the words in the domain name, while SEOs care about the backlink equity. If you are a domainer, you should look at Estibot, Domain Index or Valuate scores. If you are an SEO, you should look at the Ahrefs, Moz and Majestic metrics to gauge the value of the backlinks. Once you have figured this out, you should look at these numbers for every domain you find on GoDaddy Auctions. Do not be afraid of bidding on the Closeout auctions, as you can get good domains for cheap.

I registered for backordering with GoDaddy last year, as i saw goddady was the registar of the domain i wanted. However when the deadline for renewal came, i got a message the expiration date had changed to expire… well, a year later, i.e. now in 4 days. How can the expiration date be postponed? Was that the registrant renewed? does that mean the domain never becomes available and never goes to auction?

Registrants can also check the expiry date of their domains themselves via a WHOIS lookup. WHOIS data includes who owns domain, registrant contact details, when the domain was purchased, and when it expires. WHOIS is not a centralized database; rather, the data is maintained by the various registrars and registries that are certified by ICANN (Internet Corporation for Assigned Names and Numbers).
Here's an old post on search engine roundtable that claims google's policy is to discount previous backlink juice when a domain changes ownership.  I'm not convinced whether this is actually true or something Google says to discourage excessive domain buying / 301 redirecting for SEO benefit.  The comments above seem to give varying opinions on this matter. Would be great to get to the bottom of that one!
We do not only have Expired Domains, but you can also find lists of Deleted Domains for a lot of TLDs. Deleted Domains or Dropped Domains are available for registration and can be picked up for just the normal regfee at your preferred domain registrar! All Domains have the typical SEO relevant data, like Number of Backlinks, Archive.org Birth Date and a lot more.