So you've mastered the PLA that came with your printer, and your ready to go forth and use more advanced materials. You look online, and everyone says you need new hotend, or a glass bed, or a silicone heater pad in order to do the things you want to do. Why? Says who? What if you don't do that?

Long story into a short answer, it's bad if you don't. The hardware that shipped with your printer is very good at what it is intended to do, part of the reason why the Mk8 Teflon lined hotend has become the de facto standard for hotends on consumer machines. This is even more evident on budget machines, such as the ever-present Creality line of 3D printers. The Teflon lined hotends are objectively better than their fancier counterparts when printing within the safe range of the hardware, and it is much easier to use than the all-metal alternatives. What it is not so good for though, is pushing the envelope past the safe point. Even once you buy, install, and configure your brand new hotend you can't just go crazy with it. Your Thermistor will fail. Your bed heater will fail. Eventually you can reach printing temperatures that structurally weaken the aluminum heat block on the hotend, bordering on melting it. Every part on the machine has a failure point, and you do not need to change them all. It is not a good idea to gut your 3D printer just to "make it better", rather you should let the needs and desires material-wise guide the modifications made to the machine. It is important, however, to know where those safe limits are. Knowing your limits make it eaiser to operate the machine in a safe way, and arms you with knowledge that is helpful for when it is time to exceed those limits.

Hotends

First stop, is Teflon really that bad?

As mentioned earlier, no. Teflon is awesome as long as you play by Teflon's rules. It is a great thermal isolator, is the closest thing to a frictionless surface you can reasonably get, and is resistant to relatively high temperatures. Relatively is the key word there, in that the hotend of a 3D printer is really REALLY hot by definition. How hot is too hot for teflon? The simple answer is 245-250c. Probably.

Probably? Probably. Teflon is generally accepted to be used in temperatures up to 260c, however it is important to consider inherent inaccuracies in the printing process. Most importantly, the fact that the thermistor reading are relatively and extremely difficult to verify independently. This means it is not unreasonable to expect the temperature readings to have a margin of error, requiring the inclusion of a "safety net". (Read as, up to 260 at your own risk).

It is noteworthy that there is a source that claims much lower safe temperature maximums called the Enviromental Working Group, however this is likely to not be a representative source for safety information.

Why not just cook it? Teflon fumes can make you sick, refered to as polymer fume fever or "Teflon Flu" in an acute setting. PFOA, which is a chemical used in the production of PTFE, is considered a possible human carcinogen. This led to PFOA being banned in the use of Teflon in the United States, however I cannot find any evidence of a similiar policy in China (Where your white stock PTFE tubing was probably manufactured).