Yes, personally I think it is useful to convert. Not sure if you can do so in the GUI (change from monlithic to split disk) but you can do so using the vmware-vdiskmanager command. Be aware though that for the change to another disk format you'll need:
a) a good backup of your VM
b) enough free space as your converting your original VM that means that if your disk is now 70GB in size, that you need a bit over 70GB free in order to be able to complete the disk change.
The command can be found under folder:
VMware Fusion Tech Preview.app/Contents/Library
Executing it without any parameters will give you the help for how it works.
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Wil