HP/Level or Flat HP seals.

So Ive been buying scaling hp seals because they're half the price of the flat hp seals and flat hp gives you 8 hp (x9 is 72 hp extra at level 1), but with scaling hp seals you'll have the same hp value at level 6 then you would with flat hp. This sounds really confusing, so heres it in simple terms: Level 1 base hp with flat seals = x+72 Level 6 base hp with scaling seals = x+72

So my questions I guess are

Why do supports often prefer the flat seals over scaling? I understand it makes your all ins before 6 very slightly safer but it seems like having an extra 216 hp at level 18 would be better than having 72 extra from 1-18. Are they really worth the extra 400 ip each for that level 1-5 (when odds are you won't even be able to all in before 6 in a lot of matches)