ASM and using more than one diskgroup

I am currently using ASM with 1 production database. are there any reasons
why I would consider using more than one diskgroup? This is just an opinion
based queston. One reason might be if i want to spread IO on different
disks.

I am on a SAN. I have my SAN administrator present me space as follows

Raid Group 1 -> Lun 1-> Linux Partition 1
Raid Group 2 -> Lun 2 -> Linix Partition 2

I can use the different diskgroups to spread out my IO. Or would I want 1
diskgroup and then enable oracle striping and mirroring ?

This design is in contrast to just creating a black box on the SAN where I
might get multiple Luns, but I don't know what disks/raid groups they are
pointing to.

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