Beastmen Seals

[Flying Mullet]

What exactly are Beastmen Seals used for? I know that you are supposed to save them as they are valuable at later levels, but what are they used for at later levels?

[Citizen Bleys]

Propping up tarutaru desks.

[Ichy]

You use them to purchase summoning orbs from an NPC in Jeuno. It has nothing to do with the Summoner job. What these orbs do, depending on which one you trade in for, is allow you to go to a Burning Circle (like the one where you kill the dragon for M6) and enter a tough fight with a NM (and it's flunkies). The popular term for doing this is BCNM (Burning Circle Notorious Monster). These fights are level capped and some of them (BCNM 20 and 30) restrict you to a PT of 3. Doing these can net you some awesome rewards in terms of money and rare items. More info at Allakhazam ;)