Upon casting a magical blue magic spell, the effect is consumed, regardless of whether it was successfully used in a Magic Burst. In fact, Burst Affinity is consumed when any magical blue magic spell is cast, even enhancing blue magic spells. Burst Affinity is not consumed, however, when casting a healing blue magic spell.
Spells under the effect of Burst Affinity are eligible to be enhanced via Magic Burst, even if the Skillchain is closed by the user. Note that spells that require 5 or more seconds to cast are generally not eligible for self-bursting, since the window for initiating a Magic Burst is approximately 5 seconds from the closing of the Skillchain.
The effect of Chain Affinity and Burst Affinity are not mutually exclusive, and can be readied at any time prior to the casting of their respective spells.
In addition to the above effect, Burst Affinity will also double the Status Correction modifier (ST) of your next magical Blue Magic spell, effectively enhancing the potency and accuracy of magical spells that are modified by primary attributes (INT, MND, CHR). See Calculating Blue Magic Damage for more details.