In a case based on circumstantial evidence, motive is relevant, but also, there is no rule of law that absence of motive would ipso facto dismember the chain of evidence and would lead to automatic acquittal of the accused. Weight of other evidence need to be seen and if the remaining evidence is sufficient to prove guilt, then motive may not hold relevance, but also, complete absence of motive is certainly a circumstance which may weigh in favour of the accused.
Motive loses all its importance in a case where direct evidence of eye witnesses is available, because even if there may be a strong motive for the accused person to commit a crime, they cannot be convicted, if the evidence of eye witnesses is convincing, clear and reliable. Here, motive will lose its relevance and evidence of eye witnesses will be given importance.
In case involving direct evidence of the commission of crime, motive has little role to play as presence or absence of motive is immaterial if the commission of crime stands proved through other evidence. However, in case purely based on circumstantial evidence, the absence of motive could raise serious question and might even render the chain of evidence as doubtful and would give benefit to the accused.