I believe Tracee's murder was important to the development of other characters in the series. I know the events below are not news to anyone, I'm just making a summary to show how Tracee's murder escalated into multiple storylines....and eventually Ralph's own murder.
Tracee was pregnant with Ralph's kid, and he wasn't going to marry her, imo. Was he going to pay child support to an unfit mother for 18 years- I doubt it. Plus, she had her child taken away from her due to burning him with cigarettes- so she also had a mean streak. As a viewer, I was anticipating something bad to happen to Tracee- which finally did. Sure, it was sad watching a young, pregnant mother get beat to death, but that was how Chase let us know the extent of Ralph being a sick, violent sociopath.
Her murder caused Tony to put his hands on Ralph in front of others, for disrespecting the Bing. This led to Ralph turning down a drink with Tony in front of everyone. At this point, Tony considers whacking Ralph, but his earning capability is a deterrent.
The Tracee murder carries over to Thanksgiving. Tony comes up with a fake alibi so he can disinvite Rosalie and Ralph. Ralph meets with Johnny Sack and stupidly says that Tony is "not leaving him with many options". So, now Tracee's murder has escalated to Ralphie kicking around the idea of whacking Tony, and vice versa. Ralph said "first of all, she was a whore", implying that a stripper's life wasn't worth much- showing us how demented Ralph was in the head.
Meanwhile, there is a cold war going on between Tony and Meadow, stemming from dad's racist view towards Noah. After realizing the similarity in age between Meadow and Tracee, Tony realizes how fragile life is and apologizes and makes up with Meadow.
Before Ralph died, the karma gods seemingly responded to Tracee's murder when his son was shot by an arrow. And Tony didn't simply kill Ralph over a horse. He killed Ralph over the events leading up to it. Ralph's whacking led to the anger of some captains towards Tony for clipping a capo, or towards the Lupertazzi's if one believed Tony's alibi.
