what do the secondary butterflies do

I keep reading about people removing the secondary butterflies and the pair system.
I gather the pair is a emissions device but what is the function of the extra butterflies
Cant imagine Id need more power than it has but it is does have a very slight surge at constant light throttle which I would like to get rid of.

The secondary butterflies are controlled by the engine management system. They are supposed to, according to Suzuki, help with air flow dynamics and produce a smoother and more linear power delivery.
Whilst you control the primary butterflies with your right wrist, the ecm opens the secondary butterflies as it sees fit. So, you can crack the throttle wide open and not have the handle bars hit you in the face, because the secondaries restrict the air flow.
General concensus is that they are a device used to control intake noise and help meet emission standards, and not really good for performance. Removal, de restricts the intake tract and gives you total control of throttle opening.
The surge is most likely due to the fuel mapping. Again, in order to meet emission standards, Suzuki used a little trick. They made the fuel map a bit lean around the rev range that emissions are tested at.
An after market fuel controller will sort it right out. Dobeck EJK does a great job. Plug and play less than $200.

Thanks for that, I cant imagine how the engine can run needing a certain airflow if the secondary butterflies are not opening while the primary's are, very odd
removing them makes it run leaner without a re-map I guess?
I will look into Dobeck

They are purely for smoother throttle response. I've removed mine and the only slight side effect is the engine braking isn't as good without the secondaries. But the front wheel comes up very easily once htey've been removed

The original map is lean on the bottom end. Once you start modifying your bike it's best for the longevity of your motor that you get an aftermarket fuel controller such as a Dobeck or Power commander. There are a lot on here with Dobecks, but Reardo and I can vouch for Power Commander too especially once properly dyno tuned transforms the power delivery of the bike.