how important is wheel and tires balancing
Yes you do need to balance new tires. If you just put them on unbalanced your car may develop a vibration while driving, especially at highway speeds (60 mph / 100 KPH) Also this vibration will, over time cause uneven or abnormal wear on the tires and shocks / springs. It is usually not very expensive, usually $5.00 or so per tire and you will not have an annoying vibration while driving.
Yes. New tires are NEVER 100% true and balanced around their circumference. Neither are your rims. A combination of those two NEVERS makes for a very unstable wheel combination. A bouncing tire makes for difficult steering control, noisy and uncomfortable ride, and early tire and shock/strute wear. Shocks/struts should only move when you hit a bump on the road. They are not designed to take the bump out of an unbalanced tire.
It's a sign of tread separation. That is the tread is separating from the carcass of the tire. It will go flat unexpectedly. Wheel alignments are necessary due to a tire change. Alignments are needed if unless it hasn't been done is quite a while, or if you have hit a severe bump in the road (at least have it checked).
