I think the general opinion is do both while it’s in the garage as it will probably be cheaper than two trips to the garage, and one weak spring and one new spring will affect the handling.
As I do my own repairs the first doesn’t apply to me, as for the handling didn’t notice any difference.
As for tyre wear no problems, but you should get the tracking checked afterwards.
I even drove the car for a thousand miles with the spring broken; it was only a small piece that broke off and apart from the rattle no adverse effects.
I bought two springs with the intension of replacing both, but as with most things in my life, if it isn’t causing me a problem and I don’t really want to do it, I don’t get around to it.