This is one of those expressions that were learned through osmosis by the few people who do use it, so it's hard to convey what exactly it means though you have a gut feeling for where it does and doesn't belong in conversation. Roughly speaking, vis a vis seems to mean "with regards to", or "compared to". It's a phrase you toss in to relate two things when other tying-together phrases seem awkward or incorrect.

In a few cases, the timing of the viral attack vis a vis the backup schedule was such that no clean version of the file was ever backed up.

You could use a simpler syntax, but then you'd be wasting sentences and maybe come accross as using patronizing 'baby talk'.

From the Why do eggheads talk like that? series.