Hi @Lsim,
Most brands that I’ve subscribed to that operate solely within the US have their lists set to single opt-in for obvious performance reasons (i.e. less risk of people forgetting to opt-in via email and not make it into the list).
That said, because there’s a compliance component involved, I can’t provide a recommendation as to whether or not you should enable single opt-in for your brand. For example, there are certain countries (e.g. I believe Germany is one) that require it if your business operates or sells to residents within their borders.
If at any point you begin to experience bot activity or receive a lot of invalid email addresses, double opt-in is a great way to make sure your list remains healthy.
I hope the above helps, and congrats on the move to Klaviyo!
Cheers,
Bobby