What's the purpose of local storage hdd in Blade servers with virtualization?

I'm designing lab with a Dell M1000e and 3 M620 blade servers. Each blade server has 2 local HDD of 130GB on RAID 1.

My first attempt is to install ESXi in an SD card or USB key so my local storage is empty.

The question, what's the purpose of local HDD in this blade server? I mean, I have a SAN network with XX TB so this 130Gb looks ridiculous. Apart from installing ESXi to the local drive instead of the SD card, is there another use for this local storage?

EDIT: I just inherited the devices from previous tech guys. I just trying to understand why they bought local storage.