Every cat no matter how independent they may be needs an ID tag. If they are stuck in a neighbor's tree how will the fire department know who to bring them home to? (There are still fire departments that will rescue a cat.)
Tags are really backup for a microchip. An immediate ID is important but tags can fall off and a microchip is a permanent solution. Vets can do this and different rescue groups will do it, even pet fairs usually have someone on hand to microchip.
Free-range parenting has gotten a lot of press these days and you know the question of whether to let your cat roam the neighborhood is right along those same lines.
Is it safe? Some indoor/outdoor cats live long healthy lives, but tons don't. They meet their fate through car accidents, animal attacks, and malicious humans, not to mention the possible exposure to many infectious diseases. You can build a screened-in area where your cat gets the benefits of being outside with the sun and fresh air while staying safe from the predatory environment.
Say what you will but secondhand smoke kills and it can kill your cat. Your cat has teeny tiny lungs, so while you are huffing and puffing and blowing all that smoke, your cat is choking and just trying to breathe. Lung problems and cancer occur more often in cats that are around smoke.
Deadly trash
Your trash can kill your cat. A cat that has access to trash cans can get string wrapped around its neck and swallow things that are deadly. Make sure your trash cans are covered.
Vaccinations are the one thing that will not only protect your cat but also prevent it from transmitting diseases back and forth with other cats. Feline leukemia is preventable yet it is a common issue.
Breast cancer in cats is another disease that can usually be prevented. Cats that are not spayed are at higher risk for mammary tumors (breast cancer) as well as a potentially fatal uterine infection called pyometra.
Males that aren't neutered are more likely to fight and escape the house to roam, which makes them more susceptible to getting hit by a car or attacked by another animal.
Prevention means you stop something before it happens and taking your cat to a vet offers you the opportunity to have your cat checked for any ailments before they get to a stage where they aren't treatable.
You can see how easy it is to kill your cat, or in reality how easy it is to keep them alive for a very long time by taking all the precautions necessary and being proactive in their care.