FFmpeg scaler flags: full_chroma_inp, full_chroma_int, accurate_rnd ?

Hello,

I am downscaling some 4K videos to 1080p with FFmpeg.
Both input and output should be standard H.264 - 8-bit, YUV 4:2:0.

I'm not quite sure if I understand the meaning of the following scaler flags - could you help me with these?

• full_chroma_inp - this forces scaler to treat the input as full YUV 4:4:4, right? So it doesn't make sense to use it in my case?
• full_chroma_int - this is about using the full YUV 4:4:4 for internal processing when rescaling? Would it change anything if I apply -pix_fmt yuv420p afterwards anyway?
• accurate_rnd - "Enable accurate rounding". I assume it is somewhat slower but more precise mode? Which would result in a slightly sharper result?

Thanks!