Whats the point of ranking

I need some clarity here… I'm heading to IBOLC on November 7th (anyone else going and need a roommate?). I've also been told that I'm assigned to First CAV at Fort Cavazos after Ranger School.

Here's where I'm confused: if getting your Ranger tab is typically what secures a platoon after graduation, what’s the significance of ranking very well (like top 10) at IBOLC if I already know my soon to be unit? Of course I want to stand out to my BC at my first interview and of course I want to be proud of myself, but obviously what I do at my unit as a PL a year from then will stand out more than past IBOLC/ranger recognitions.

So if I'm set to join First CAV and just need to perform well enough at IBOLC and graduate Ranger, is there really a point to pushing for top rankings at IBOLC? Or am I missing something about how it all ties together?"