All-pass filter usage in automotive room correction
Allpass filters are very helpful in automotive mainly for getting the imaging dialed in. You often need to time align the contributions of different driver groups (left, center , right) at a specific listening position. Due to the complicated acoustics of the cabin. the delays are often dependent on frequency and so all passes can be very helpful in correcting this.
Allpasses in cross overs are typically not that useful, since the range of overlapping frequencies is pretty narrow and you can typically get by with a single delay