The adverb is the part of the language that qualifies a verb. For example, "I am going to see [verb] her today/tomorrow/daily/weekly/monthly/yearly [adverb]."

So why waste space and time by saying/writing "on a daily/weekly/monthly basis"? Or perhaps even "on a today/tomorrow basis"?

The "on a basis" is another construction much loved of the usual suspects, including politicians, social workers and journalists/broadcasters, whose grey matter has become white matter - cotton wool - "on a temporary/permanent basis".