After a forward jump and after using LK, Ibuki can follow with her aerial MK. This performs a 2 hit combo. This attack has a spiritual successor in the Street Fighter V series in Tobikura with the same ending.
While most cross-up attacks are done with MK, Ibuki's main cross--up is LK. This means Ibuki usually has less hitstun to followup an attack than most of the cast. This also means she has less blockstun than most of the cast when landing meaning she could be counter attacked at some ranges. This target combo is great for increasing blockstun and damage on fake cross-ups. Some opponents can even be hit twice on a real cross-up.
In the SFIV series, there is no way to combo into Target Combo 3. It's sole function is increase hit and blockstun (alongside damage) to fake cross-ups.
In Street Fighter X Tekken this target combo perfectly aligns with Target Combo 8 to form much of Ibuki's offensive core. This target combo is perfectly made to extend Target Combo 8 and land a Raida, Super, or just gain the position she wants with Kasumi Gake.