In practice, you rarely need data in visualization files that's more accurate than, say 3 valid digits. In that case, ASCII is -- maybe surprisingly, often more compact than binary form. If you're thinking about archiving, the bzip-ing these ASCII files is likely going to yield the smallest files you can get.

That said, Paraview reads VTU format which has a compressed binary form (XML-based, but the data is first libz-compressed and then uuencoded again to yield ASCII text). On typical files, this saves a factor of 4-10. For large files, this is definitely the way to go.

In practice, you rarely need data in visualization files that's more accurate than, say, 3 valid digits. In that case, ASCII is -- maybe surprisingly -- often more compact than binary form. If you're thinking about archiving, then bzip-ing these ASCII files is likely going to yield the smallest files you can get.

That said, Paraview reads VTU format which has a compressed binary form (XML-based, but the data is first libz-compressed and then uuencoded again to yield ASCII text). On typical files, this saves a factor of 4-10. For large files, this is definitely the way to go.