Verified answer

The best thing to do is bleed until you see nice clear fluid as well as no bubbles. Brake fluid will take moisture in from the air, then it can boil that moisture in the caliper and line when the brakes get good and hot. The fluid itself can get too hot and turn dark.

Remember to top off when doing this so you don't run the reservoir dry.

Even a tiny amount of air will cause spongy pedal. The brake system relies on hydraulic pressure, which allows pressure to be distributed evenly throughout the system. Since brake fluid cannot be compressed, as soon as you step on the brake pedal it transmits that pressure through the brake system. And since air is compressible, the air bubbles will compress when you step on the brake pedal and take some of that hydraulic force away causing reduced brake efficiency and spongy pedal feel. You must remove all air from any hydraulic system in order to get full efficiency from that system.

Keep in mind, however, that you may see a few air bubbles while bleeding you brakes due to air being sucked in around the bleeder screw threads.. That does not necessarily mean the air came from within the system itself.

Absolutely. Zero air!

could be a defective brake servo.. bleed the rear brakes first undo the nipple and pump the peddle ten times ,hold pedal to floor and tighten nipple.

any air is bad, bleed it totally, and top up your fluid