it doesn't. it might if you're multiplying numbers in the thousands of digits (but even that is almost assuredly too low). for essentially everyone this is purely a theoretical result.
You're dramatically underestimating. You need something like 2^2^2^5000 digits or something crazy like that.
yes, but even the dramatic underestimate shows how useless it is. I also imagine that current estimates could be significantly optimized if there was some usecase for them. the 1k-10k multiplication regime has actual usecases, so there has been some optimized implementations of theoretical integer multiplication algorithms in this regime.