How old is your home? Has it been rewired? If your home was made in the early 1900s it most likely has the knob and tube method of wiring used in that time period. Is it safe, or has it been modified, what kind of modern units are you using in your home such as air conditioners, dishwashers and dryers. These are all questions you should be asking yourself if you are a homeowner and want to safely use the electric it the house. I have done some research on this wiring method and will contrast the goods from the bads to see if it should be replaced or if its better than standard romex.
First, if there is old style wiring in your home does it last. The knob and tube wire i have messed with has always been aluminum. Its a good conducter, but it is flimsy. If you tug on it just i tiny bit it will bend or adjust in a different position, witch could be bad if a switch is wired behind the wall and you can not see the wire to adjust it. So if it has not been messed with it is usually in decent shape for an example if you put a new receptical in and you have knob and tube wiring it might be weak and break.
Standard romex on the other hand is more durable to weathering because instead of clothe it has rubber insulation that can withstand weathering better than cloth. Also its made out of copper wire that is more resistant to breaking. You can bend and straighten the copper wire over and over and it will still be good to use. They also make different types of insulation for romex if you are placing it somewhere that is exposed to the weather. So thats a plus for romex againts knob and tube wire.
Secondly knob and tube wiring used fuses verses romex using circuit breakers. A breaker or a fuse has the same concept. If the amps in the circuit get too high it would blow the fuse or kick the breaker to where it breaks the contact in the power panel so that circuit would not get power. For example if you got circuit for a fridge on a 15 amp fuse or breaker and the fridge requires a 30 amp it will kick the breaker or blow the fuse so it does not overload the circuit and create a hazard. Everything in your house thats wired for your oven or your dishwasher has a load it needs to get or it will not run properly. So who ever wired your house counted everything and the amps you needed and if its on a breaker and you overload it, it will break the contact. But for the match between fuses and breakers is even because they both do a job just fuses you have to replace and breakers you just reset.
Romex is is copper and most of the knob and tube wire is aluminum. They both can carry the same amount of watts/volts depending on the gage or size of the wire. But the copper last longer if it gets hot. For example the aluminum gets hot and it wants to bend and over time it could move than settle move and settle ect.. After time of doing the it could come...