I have a Mac with OS X 10.10.5 on a HD which had 4 partitions.
Using Disk Utility I deleted one of the 4, intending to slightly grow the 3rd (containing the OS), leaving space for a new partition to install El Capitan.
This has been my practice up to now when a new version comes out.
I booted to another HD and deleted the partition, but it then proceeded to resize the 3rd partition YoodenVranx to use all the free space.
There seems to be no way to change the Partition Layout, or resize the partition.
I rebooted and used diskutil to list the current state.
/dev/disk0 #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme *500.1 GB disk0 1: EFI EFI 209.7 MB disk0s1 2: Apple_HFS Fenchurch 80.0 GB disk0s2 3: Apple_HFS BxxxxxData 70.0 GB disk0s3 4: Apple_CoreStorage 349.0 GB disk0s4 5: Apple_Boot Recovery HD 650.0 MB disk0s5 /dev/disk1 #: TYPE NAME SIZE IDENTIFIER 0: Apple_HFS YoodenVranx *348.6 GB disk1 Logical Volume on disk0s4