Question: It has been said many times that the Coordinator is not necessary because its confirmations will be rejected by other nodes if it acts maliciously.

It follows that if other nodes can tell if the Coordinator acts maliciously, then in fact they do not need the Coordinator.

According to [The Transparency Compendium](https://blog.iota.org/the-transparency-compendium-26aa5bb8e260):

> 
> This does not mean that the IOTA ledger is currently in any way
>  centralized, the network is 100% decentralized, **every node verifies
>  that the Coo is is not breaking consensus rules by creating iotas out
>  of thin air or approving double-spendings**
> 
> 
> 

According to [eukaryote31](https://webcache.googleusercontent.com/search?q=cache:0-PjedmiS5EJ:https://www.reddit.com/r/Iota/comments/7c3qu8/coordinator_explained) (respected person within IOTA ecosystem):

> 
> What if the Coordinator started acting maliciously? Every node looks
>  at the transactions it gets and only tells other nodes about
>  transactions that are valid. **The Coordinator is no exception, if the
>  Coordinator starts issuing bad Milestones, nodes will just reject
>  them.**
> 
> 
> 

According to [iota.stackexchange high rated answer](https://iota.stackexchange.com/a/7):

> 
> The Coordinator is no exception, if the Coordinator starts issuing bad
>  Milestones, nodes will just reject them.
> 
> 
> 

This begs the question, "what makes Coordinator Milestones a security measure if the other nodes are already doing this?"

Answer: 
There is a link between milestone frequency and average confirmation time. But the time interval between milestone is not a lower bound for confirmation time. 

If you submit a tx, and if you are lucky this tx can be immediately selected as tip to approve by a new milestone and you will have a very short confirmation time.

Establishing the exact relationship between milestone frequency and average confirmation time is probably too difficult because many factors comes into the equation like :

* tps
* rate of unfair transactions (i.e. transactions not using the random walk to select tips)
* alpha value
* network topology
I think while we have coordinator fastest confirmation time is limited by frequency how milestones are issued. By definition. Because to be confirmed = to be referenced by milestone.
Average confirmation time must be strongly correlated with the milestone frequency too