we will use the passive crossover of component speaker as example.

Say if you have a full range signal you dont want low frequency signal to go to your tweeter, or high frequency (above 4Khz) to go to your midwoofer right? It filters out frequencies.

Advantage? If you use them you wont worries kahit anong tuning gagawin mo your speakers are safe.

Dis advantage?- extreme tuning limitations if you're a hardcore SQ fanatics that listen to a very finest detail of frequencies and those who compete like EMMA they ditch the crossover and go full active. They have full control of the frequency cutoff and slopes.

Dont get me wrong some people compete also using passives but less tuning control.. or other built it by them selves and set the desires cutoff in the passive.

HTH