A lot of things such as OTC cough medicine and some opiods contain the active ingredient of Tylenol so that's a good use case for avoiding it. Ibuprofen has issues of its own, but IIRC it's typically safe to take 2-4x the recommend dose on the bottle, which could be pushing it if you did the same with Tylenol over an extended period (especially if you're a drinker). I've heard anecdotally that if Tylenol were invented today the FDA wouldn't approve it because it's relatively easy to OD.

Meanwhile, doctors I've been to offer out prescriptions for 800mg ibuprofen pretty freely and don't seem too worried about side effects (IMO it's easier to just take a bunch of the smaller ones instead of a single horsepill)

To be clear, the message (which I'm passing on second-hand, I'm not a doctor myself!) wasn't that you shouldn't take Tylenol, just that you need to be careful with the dosage. My father in particular thinks Tylenol is better than Advil if used regularly over decades (although he'd probably say it depends on other health conditions too; both are safe medicines overall.)

Neither Paracetamol (Tylenol) nor Ibuprofen (Advil) is side-effect free - and thus you should stick to prescribed amounts unless you've received medical advice.

Having said that, given I am not a doctor/clinician/pharmacologist/pharmacist, you can usually alternate them to take a higher dosage of pain relief.

"always" is too much of an absolute. It really depends on a variety of factors, not least if which are other medications you might be on and underlying conditions. For example, ibuprofen doesn't play nicely with prednisone. Or if you have any sort of existing liver problems then acetomenophen is really not a great idea.

If you have a regular doctor, it's probably a good idea to ask which of a few different options are safe for you for occasional use, and probably check in if you find yourself needing something for longer than a few days. (And if you don't have a regular doctor, find one... If you lack insurance, it's still probably worth the money to pay once a year for a physical, and also have a resource that knows your health history that you can consult with. For basic questions, like "does my medical history rule out acetomenophen", most doctor's offices will take a message for the doctor and then call you back with an answer)

No-one here can answer that because the only people qualified to do so (pharmacists, doctors, some nurses) also have a professional duty preventing them.

The answer is "it depends" on your history and any other meds you're taking and also your home situation.

If you're Asthmatic (it's generally not advised to take Aspirin or Ibuprofen as you could be allergic to it), if you have an ulcer, if you're on a blood thinner such as warfarin.

Ask a doctor. They are qualified to give you the right answer based upon symptoms and medical history.

Either is fine as long as you follow the instructions on the bottle.

IIRC you can take them both on interleaved but overlapping schedules, for those times when the maximum frequency of advil isnt good enough. Check on that before doing it though.