How to set a low gass and let it wait without failed transaction

I have got mixed messages when reading multiple posts.

Some say if you keep Metamask's gas price low, but dont change the gas limit, the transaction will be pending (days or weeks) until the gas price is low enough to send this through. This is one way to save gas fee if you are not in a hurry.

Some others say they reduced gas price but ended in a failed transaction, plus being charged for gas for this failed transaction.

Which one is true? Is there soemthing special that needs to be done to avoid failed transaction, in addition to lowre gas price but keep gas limit?