I like the explanation from the release notes: "SP-GiST is comparable to GiST in flexibility, but supports unbalanced partitioned search structures rather than

I like the explanation from the release notes: "SP-GiST is comparable to GiST in flexibility, but supports unbalanced partitioned search structures rather than balanced trees. For suitable problems, SP-GiST can be faster than GiST in both index build time and search time." Basically operations in SP-GiST are generally faster than in GiST, but due to SP-GiST not being balanced it does not fit all problems. I would guess SP-GiST is really good at geodata like in PostGIS, since coordinates are relatively evenly distributed in space.