When you import LR by default creates standard previews. This is what you see on the screen not the actual RAW. When you click on one to make it full size it creates a 1:1 preview.
For what it's worth, when I import I set the preview size to 1:1 in the build previews option box. It takes a little longer to finish the import but after its done flicking through images when reviewing is much faster as the previews don't need to be created.
Also yes the 1:1 previews will take extra space, but I would be odd if you had space for lots of RAW files and not enough for the previews. Also when LR does your weekly optimisation/backup by default it removes those over 30 days old.
I was under the impression that minimal is the default setting and that standard are created when you click to go full screen. One to one are only created when you zoom to 100%.
I run my operating system on an SSD, raw files get stored on a hard drive. Space on the SSD is limited and expensive . Space on the hard drive is large and cheap. Ideally everything would be on the SSD, but that's not going to happen until SSD prices drop some more.