Explain -gc 1 and -gc 2 and loading times

6-9 months ago game was crashing alot for me in Act 2 when changing zones.
USing -gc 2 for the poe.exe shortcut made the zones you visited already load faster.

But what exactly those 2 options do?
Are they still good?

I will play HC.

Also how can I improve the game loading time... it takes me 3-4 minutes to get to the login screen

bump

Takes me so much to get to the exe login area...