Type 1 files contain separate information for each track. For a Type 0 file, however, all the tracks are merged into a single track, although MIDI channel information is still retained. When a Type 0 file is loaded into a sequencer, it will take each channel's information and put it on a separate track. So for a typical sequence with one track per MIDI channel, it will normally not matter if the sequence is saved as Type 0 or Type 1. But if your source sequence has several tracks assigned to the same MIDI channel (for example several drum tracks playing the same program on the same channel, but with an individual drum sound on each track), then it is best to export it as a Type 1 file. If exported as Type 0, all tracks assigned to the same channel will be merged into a single track when the .MID file is loaded.