If they open a joint account, the funds automatically go to the other party on the demise of the other. So if they are both ok with that, nothing to worry about. But if they intended to leave (for example) half of their estate to their surviving spouse and the other half to their kids, the funds in the joint account do not form part of the estate. The surviving spouse gets it all. They may want to consider that too.
Would definitely recomend joint accounts. My parents had every thing separate. My mother paid half the household bills. Dad paid the other half. After my father died, the folks at Ulster Bank were horrible to my mother. She was fine with not being able to access the funds in his accounts until after the will was probated. My dad was a bit of a messer when it came to money, so she just wanted to sort out anything that needed sorting. She just wanted information on the account such as did he have any outstanding standing orders that needed paying by her now, depositing pension checks into his account, was his account in overdraft etc etc. The bank manager refused to even speak to her, answer her letters or return any of her calls. He would only speak to the executor of Dad's estate. As he was overseas for 3 months after my Dad died, she was in utter limbo land for ages. That would not have happened if they had joint accounts.