Their primary purpose is to pay the costs for your Pokmon's actions
The most recent Secret Lair drop featured foil constellation versions of the original Theros Gods, and there was a bit of a debate about whether the cards should be compared to their original foil value (which is quite high) or non-foil value
Its also gotten stricter over time, according to SGC grader Derek Grady, who told Sports Collector Digest in 2019 that In the early days of PSA, cards that were graded an 8 for the most part now if you cracked them out and resubmitted, they would grade lower. Nowadays, PSA uses the half-point system that many other services in the card grading industry also favor, which can be broken down like this: PSA 10 / Gem-Mint (GEM-MT): a virtually perfect card, according to PSAs website
On the other hand, you could also open a pack full of draft chaff and end up pretty disappointed
Set up practice scenarios: if your Pokemon has 80 HP and is poisoned, how many turns until it's knocked out
11 Sovereign Okinec Ahau Watch It Spiral Out Of Control It can take a turn or two for Sovereign Okinec Ahau to build up, but once it does there's very little your opponents can do to stop you from taking over the battlefield