I remove all the white inserts, but I keep them. I use them for practice, or often print my own backgrounds on them with my wide format printer. They could also be stamped, misted, etc. to use for the base paper. Sometimes I cut embellishments out of them. Anyway, I save and use the inserts.
If you're using pp, you'll have two in one protector (one for each side's lo), so it is sturdy enough w/o using the white sheet. With cardstock, sometimes I use both sides, but again, often use a different pp or cs on the other side. There is room in most protectors for two pieces of cardstock, plus embellishments.~Judy
Oh...and welcome to the site!