Generating Session-IDs when booting Computer - why not?

I came across a question on the disadvantages of generating a pool of random session ids everytime the computer boots. When a session is over the session id is being put back into the pool.

The only disadvantage I can think of is the limited number of sessions possible but other than that none.

Do I miss something because it feels like there are more disadvantages but I cant think of them.

FYI: its not a homework or assignment. I‘m just studying distributive systems and came across the question