Hi Team, I know SuiteTax needs to be enabled if the account would be utilizing multi subsidiary customer. My question is my client currently has AvaTax, does enabling suitetax affect our existing AvaTax in any way? Also, do we need to configure SuiteTax or can we just have it enabled.

Definitely don't just enable SuiteTax without getting more answers, because you can't turn it off. For some providers you need to get a different version of the software for SuiteTax, but I don't think this is the case for Avalara. I suggest you work with your customer to ensure they get support from Avalara about this

In order to use SuiteBilling with multisubsidiary customer SuiteTax needs to be enabled. I don’t think there is any walkaround for this. However, I just wanted to know if SuiteTax interfer with SB in any way

I'm not sure what risks there might be to SuiteBilling in particular from SuiteTax, but SuiteTax is a very serious feature to turn on. Does your client use MSR (Multiple Shipping Routes or "Line Level Address")? Does your client sell any fulfillable item - even if not through SuiteBilling? Does your client use Multi-book, International Tax Reports, intercompany JEs?