Subwoofer or Bi-Amp?

Hello everyone. I was wondering which application makes more sense.

Should I buy a subwoofer or does bi-amping speakers effectively create a subwoofer situation.

It seems to me that using two separate amps, one for the midrange/highs and another for the lows creates a situation where you have a powered subwoofer without purchasing a dedicated subwoofer.

I hope that explanation makes sense. What are your thoughts? Thanks for your help.