Using hardware allows some operations like decoding, encoding or filtering to be completed faster or using less of other resources (particularly CPU), but may give different or inferior results, or impose additional restrictions which are not present when using software only.
Hardware decoders will generate equivalent output to software decoders, but may use less power and CPU to do so.
Hardware encoders typically generate output of significantly lower quality than good software encoders like x264, but are generally faster and do not use much CPU resource.
ffmpeg -hide_banner -hwaccels
returns:
Hardware acceleration methods: vdpau cuda vaapi qsv drm opencl