Why do most algorithms use sequencefile as input and output?

[Lee S]

Hi all:
  I'm wondering why the input and output of most algorithm like
kmeans,naivebayes are all sequencefiles. One more step of conversion need
to be done if we want the algorithm works.And
I think the step is time consuming. Because it's also a mapreduce job.
  For the reason to deal with small files and compress to save disk space?