Converting from lossy to lossless codec

Hi,

I have a file with 3gp and inside of it a video stream in MPEG4 format and audio stream in amr_nb format.
Just to play, I've converted video to huffyuv. I've noted that file size grew and as it is expected the actual quality didn't change.
Perhaps it sounds somewhat silly, but I'd want to know why the bitrate, fps are increased... if after all, some data are lost, and you cannot come back to the "original"

Is it right my rationale? Does make sense in some case convert from lossy to lossless codec?

Thanks in advance!