Class restricts what a character can do. So does race. And many other game mechanics that you choose.
I don't see a difference in how race class and alignment are used. They all give the players options and limitations. They're all used to force players to pigeonhole themselves in some way or another.
Those are kind of the general advantages of the systemAnd this thread isn't about alignment not causing problems (which it most certainly does, even if it's not the proximate cause), it's about alignment actually doing good when it's used.
- Giving immature players a reason to learn how to work together as a group (I've found it especially useful for kids under 15)
- Giving inexperienced role players some ideas on how to flesh out their character beyond "guy who hits things with a stick" .. there are other methods I like better, but few of them are as simple as alignment.
- Helping inexperienced players separate their desires as a player from what their character would want.
- Giving GMs a broad idea on how a particular npc or monster should be played without requiring deep thought into it.
More experienced players and gms tend to form a more nuanced view of alignment. The only time I've really seen any problems was with an experienced player who didn't realize how inexperienced his GM was.
As an example: I was playing a Balance aligned innate magic user, there were several cases where it was useful to draw on how the various alignments (Elder vs Kotothi, Sidh vs Kotothi, Law vs Chaos, Shamanic Elder vs Law and Chaos) interacted to determine how I should treat various NPCs, and where I could best serve the Balance. The party (as I recall) had members who were Balance, shamanic elder and Sidh aligned, but it's been so long I don't remember a lot of specifics.I would expect examples of players being unsure what their character, and then checking their alignment and having and interesting way forward suddenly made clear, or of players receiving useful guidance for playing characters different from themselves, or of alignment driving an interesting story element.
I seem to remember convincing my party to not aid a Law NPC Wizard as he fought some the Kotothi forces... the Sidh member of our party was livid, but we convinced him that we could always come in later and take on the Kotothi forces after the Law Wizard had softened them up, thereby weakening both Law AND Kotothi