I've seen some very competitive times on this game are done on emulator, why is this? I assume there is a reason for this. Is emulator very accurate for this game? Usually games don't emulate 100% accurately so it is making me curious.
It does emulate games 100% accurately. At least for the whitelisted emulators.
There are several pros and cons for emulator.
The main benefit of emulator is the convenience factor - you don't have to buy a NES, and a CRT, and the game cartridge, and the cables to put it to your computer, you just download FCEUX or Nestopia. Easy
The main problem with emulator is input lag - there is existent input lag while using an emulator that is not present for NES + CRT - which makes the tricks a little harder. However, your brain tends to adjust to the lag, and your muscle memory will adapt to the slight lag in time even for hard tricks like flagpole glitch.
The main benefits of console are the reduction of input lag and --- the purity of the console in its original form (if that is important to you).
The problems are that arguably using a controller can be more difficult because of the placement of the D-pad and buttons (or easier, depending on who you talk to). Also it's more work to setup, and more expensive to acquire.
Still - there are many unbelievably good runners that are almost exclusive to the emulator. @Niftski, @Lul_ecks_dee, and @Tecate to name a few. All rediculously talented.
Effective immediately, any submissions using the SNES9x emulator will not be verified. The SMB1 mod team has concerns about its integrity due to its ability to overclock and remove lag frames, which may not be easily detectable. Additionally, we request that all BizHawk submissions avoid using the S