Building materials...?

Before, after building a character's building, I used to save these because they were needed for construction or expansion. But after the White Knight, they stopped appearing. When I try to throw them away, it says something like 'becomes building points,' so I'm wondering if there's no use for them anymore? I keep getting pink potion treasure chests and event rewards frequently, so they're piling up, and I'm debating whether it's okay to discard them... Also, I wish they'd change them into more practically useful prizes 😥