This is one the questions from the definition phase and I would like to get it discussed in the main site. (으)세요 and (으)ㅂ니다 are both honorific ending. When should we use one over the other?
You're mixing two slightly different aspects of speech. One (합쇼체: ~습니다/ㅂ니다) is more of a level of formality due to setting and the other(시) is a level of respect towards the subject of your sentences.
~세요 is simply a combination of 해요체(어/아요) and the honorific marker (시). Honorifics are only used towards people of higher status (i.e. older people, individuals higher up in some hierarchy, etc..).
합쇼체, or deferential form, on the other hand denotes a degree of formality. Of course, you don't need to use honorifics in 합쇼체 unless the person you're speaking to requires so. However, you only use the form in situations like business environments, speeches, broadcasts, military settings, etc..