Advantages of crossdraw:
Excellent access for weak hand draw.
Depending on body shape, USUALLY easier to access while seated.
Excellent "orthopedic fix" when something like a rotator cuff injury limits user's ability to draw from strong side hip.
Keeps gun more inaccessible to someone in right passenger seat (i.e.,the handgun carrier who insists on picking up hitchhikers, or LEO who has to transport arrestees in department-assigned pickup truck).
I know you didn't ask, but disadvantages have to be considered alongside advantages for perspective. Disadvantages include:
In face to face confrontation gun butt is presented toward assailant.
It takes care and technique to draw from butt-forward holster on a firing line without crossing fellow shooters on your holster side, the primary reason they are forbidden in PPC and IDPA competition.
Many body shapes make crossdraw awkward and difficult.
Gun generally has to be mounted forward of hip for easy access to dominant hand, making concealment more difficult.
Hoping this is helpful,