Temp. control (TC) is a two tier thing.
Let's give you proper info:
First note: NI and TI if heated too hot will oxidize, and particles can start coming off the coil, and if you breath those in, it is very harmful, so never use either types without TC.
Second note:TC prevents the coils from heating up higher and higher as wattage mode does... once it reaches your set parameters, it stops the power and pulses to maintain the coils at your settings.
The two tiers thing: 1) Wattage is how much power you're applying and causes how fast the coil heats up. 2) the temperature set is what determines this power output to the coil using calculations from the changes in the resistance of the metal (ohms).
So when you set your mod for NI or TI, you need to set it properly according to the coil. MTL device tend to be very small coil that heats up very quick, so 7-14 Watts can be the proper range for those, while a larger type device (aka much larger coils) can handle 30-60 watts. Too low and nothing much happens and can cause flooding. Too high is going to ping the TC to hit the temperature set too fast and be a bad vaping experience with it pulsing non-stop.
That said, for the TC, the range is usually 200 to 600 max (Fahrenheit) which is the safe range.
So depending on the tank and coil you use, for example, the Aspire Atlantis/Triton, or the eLeaf Melo/iJust, Freemax Starre/Scylla all use the same cross-compatible type coils, which can be set at 30-50 watts (some higher), and temperature is usually good at starting at 420F. As the coil wears, you can increase the temp, without any risk. Note that from one liquid to another, you might need to change the temperature settings as some liquids vape better at higher temperature than others.
Personally I prefer TC to the point that I don't like wattage mode much, with TC you have a stable vape, it reaches what you set it for and gives you a much smoother vape.
The best approach when you're not sure.. start low, first with the wattage settings, and then set the temperature. If it's not working well, increase the wattage a little at a time... at some point, you'll see that the temperature you've set might be too low, so increase it bit by bit too. Takes a few minutes at first until you get a good idea about it... once you get it right, it's awesome.
Other benefits with TC
1) no dry hits, if you're out of liquid and don't notice, (or the liquid is too thick and not wicking well) the coil heats up too fast (near instant) but the mod sees this and will stop the power output instantly.
2) it can helps prolong battery life a good 10 to 30%.