This is my first build where I plan NOT to have a CD/DVD drive.
( side note : my New EVGA case DG-87 doesn't even have a slot for it )
 
I would think we need a file set in motherboard software drivers download section  to go direct to USB flash.
Could use a full ISO there as well as the separate drivers there are not a complete load set
(at least for 64 bit Windows-10)
 
(I did make a try to Office MAX and got a $30 unit )
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Device I no longer use to load my computers
1. Front panel switches in octal or hex
2. 80 col IBM cards
3. paper tape and Mylar film tape
4. Magnetic tape
5. Audio tape - and DAT tape
6. Floppy disks ( 7,5,3.5 inch)
7. CD's
8. At least we still have a headphone jack 

Try just using only the online drivers some time on a new first load :-)
Well at lease with a Windows-10 system
 
and see the "platform not supported errors" on the ME drivers
the No computer hardware with the Killer drivers
 
Best to just copy the CD/DVD  directly to a Flash
This way you still have the loading scripts and a tested driver load order.
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I was testing different device for booting Windows-10 and different raid booting so I got to do over 20 full installs.
(to be fair - I did do most install testing using the old BIOS 1.01)
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I have cats so at least I never had to ask for a replacement  DVD because the  dog ate it.