The two parameters deal with quality. They trade off space for quality. If you record with a quality-based rate control such as CQP or CRF, you have infinite space, so you can just optimize for quality if you want. B-frames are the ones with the highest compression (most detail removed), so the more B-frames you insert, the lower the quality. So to optimize B frames for quality, you should use 0 B-frames (none at all) with CQP.
With key frames, it's the same, only on a higher level and the other way round. They contain a whole frame and are an anchor for P-frames, which have a higher higher compression (less detail removed) than the keyframes (but lower than the B-frames). So if you want higher quality, use more keyframes, which can be achieved by using a smaller keyframe interval. It has the side effect that a video with more keyframes is better seekable. With lower keyframe interval, video size increases vastly.
With CBR rate control, the effect is reversed, since you limit the bitrate. To achieve the forced bitrate, the encoder removes as much detail as needed. If you don't use B-frames or use a lower keyframe interval, the bitrate is consumed completely by the bigger frames, so the general quality must be lowered, which is very visible. So don't do this (don't use CBR for recording).
