In general, VxFS works best if the percentage of free space in the file system does not get below 10 percent. This is because file systems with 10 percent or more free space have less fragmentation and better extent allocation. Regular use of the df command to monitor free space is desirable.
df_vxfs(1M) manual page.
Full file systems may have an adverse effect on file system performance. Full file systems should therefore have some files removed, or should be expanded.
fsadm_vxfs(1M) manual page.