The two attributes are pos and uv, which are almost always tied to each other (and therefore be updated together). The GPU will access attributes by index hence

The two attributes are pos and uv, which are almost always tied to each other (and therefore be updated together). The GPU will access attributes by index hence they should be interleaved otherwise you are just forcing cache misses. Indices are not vertex attributes and thus should not be interleaved with the other data.