The benefit to readers of having Elly look at a half-full glass only to stand around screaming about how someone drank it on her is that they are reassured that they are not alone in feeling as if motherhood isn't quite what it was promised. A lot of people out there like it that Elly is never going to be happy because their own feelings of disappointment are validated and also that she never got to savor her triumph because it would be like watching Charlie Brown finally kick the football.
The problem is that Lynn decided to carry this phenomenon of Elly never being able to feel happy into the bookstore. As others have mentioned, we saw no new friendships being formed and no regular customers manifested themselves as someone for Elly to talk to. All we had was more hostility, more disappointment, more of Elly being infuriated by trivialities and overreacting to minor irritation, more of Elly being the same intolerant, self-absorbed raw nerve who pissed away the best part of her life being pointlessly angry with her children for no other reason than the fact that she's a depressive narcissist who needs to feel sorry for herself. Her staff wanted her to pack it in before she ruined the place and having to bother with other people became so much of a bother that she quit and declared collecting rent from Moira victory.
While Lynn might have felt good defaming her staff thusly, what she doesn't realize is that her insinuation that it was okay for Elly to retire because she'd paid John back the money he spent buying for her made her look like a flake and dilettante. Since she never actually made a real profit and only manages to skim from someone who does, it also makes her look like someone's wifey who got bored and played at running a business. The worst of it is that she'll no more understand this than understand that a budget cut is not a popularity contest.