To be honest with you I would recommend that you always provide a tray.
So may people don't have one in the home and that means when there is a problem it is often not noticed as early as it might be, therefore causing more serious problems the longer it goes on.
Cats Protection advise always provide a litter tray irrespective of your cats age even if they are allowed out, (in fact it is a condition of CP homing a cat) if you keep an eye on what your cat is passing and the frequency the cat is in the tray, you can spot many problems, e.g. cystitis is very common in cats and needs urgent Veterinary treatment. It is often shown up if the cat uses the tray frequently and/or passes blood. A year ago it was necessary to have Trudie a long term CP cat PTS due to bowel cancer. I would like to hope that Trudie's untimely death has not been in vain as a lesson can be learnt from it, and that is the reason why everyone MUST always provide a litter tray no matter how old the cat and irrespective of the fact that it may go out. So many times I am told oh! I have no need for a litter tray my cat goes out now. Had Trudie no access to a litter tray the cancer would have continued to get the better of her and she would have suffered, she looked purrfectly well and it looked like there was no reason to take her to the vets, the only reason I took her was because I noticed she was going into the tray more frequently than usual and there was blood on most pooos and drops in the tray. None of this would have been noticed had we no tray we don't know what our little ones are putting in the hole in the garden.