No, it's an Amiga accelerator.
Without the Amiga it dosn't do anything. You could have it plugged in with just the SDRAM in there, and use the A4000 graphics output, A4000 sound output, A4000 serial port, all with no problems, and they'd work just exactly as they always have done with any other CPU card that has local memory.
However with this card, you can have high speed USB and Firewire connectivity as well, and AC97 audio for 16bit sound in/out, and 100MHz memory bus, and ATA66 IDE. All of these connect to the accelerator card.
As far as the A4000 or A3000 is concerned it's a bloody fast CPU card.
Personaly, I'd say giving my A4000 the equivalent of an 800MHz 68040 is a good thing... if it comes with extras that run at speeds appropriate to the CPU then I'm certainly not complaining...