In terms of significance, there is none. Other than that it will probably wreck her career. She has said she plans to still caucus with the Democrats, so the effect is fairly mild.
My views on moderates has changes over the years. When I was in college in the early 90s, and even shortly after leaving college I viewed moderates as people that didn’t have strong political beliefs and were mostly in congress just to milk the taxpayer. And to be honest, there were alot of those back then. There was a bipartisan middle that largely governed the country. Who was in power only very slightly changed things.
But now, we’ve become so hyperpolarized. Both parties have gone out to scrub moderates from their ranks as much as they can. Obama turned the Democratic moderate into the Dodo bird, and the Republicans followed suit and did the same with the rise of the ‘Freedom Caucus’. Paul Ryan was forced out as Speaker (yes, I know he retired, but we all know he didn’t reach that decision in a vacuum) because the reliable conservative was deemed too moderate.
Both parties have run to their extremes with computer-aided gerrymandering making competitive general elections rarer, and primaries guaranteeing that the only threat to a candidate comes from the party’s extreme wing…thus encouraging them to never cooperate and govern more extreme.
And so in the rare cases when a party member tacks AGAINST their party like Sinema and Manchin did (to some extent) in the last term, or how Liz Cheney did in criticizing the election steal loudly rather than under her breath like most moderate Republicans…or staying silent and far too many of them did…I view those moderates very very VERY favorably because of how rare they’ve become. Mindless loyalty and devotion to your extreme base has become the norm. We need more Sinema’s who are willing to look their own party in the eye and say “No.”
But going ‘Independent” seems politically suicidal. She probably doesn’t think she’ll survive her next election anyway, because doing this means the D’s will likely run someone against her in the next general election, and that will weaken her against whatever Republican is running. It’s HARD to win as an independent in our system. It was DESIGNED to be hard.