There's BUSS L/R recording, and DIRECT recording.
Each method has it's use.
The basic mixer on the 414mkII is "8x2", which is 8 inputs mixed down to 2 tracks, [stereo-L/R]. The recorder section will record tracks 1 & 3 from the Left, and tracks 2 & 4 from the Right half of the stereo mix. The PAN controls whether the INPUT is Left, Right, or somewhere in between, and therefore PAN is central in assigning the Input channels to the tape tracks, when in BUSS mode.
F/I, as you described, you only have one input and you're recording BUSS mode, panning either left or right, assigning your one input to the tape tracks.
If you're only using one input, [either a line or mic], then you could record DIRECT, and it wouldn't make a difference, as long as you plugged into the correct inputs, corresponding to the tracks, and switched to DIRECT mode accordingly.
DIRECT mode records from the input channel, direct-to-tape, such as [Input 1:Track 1], [2:2], [3:3], [4:4], as you know. DIRECT mode is useful, if you only have one input [source], or if you're recording 3 or 4 tracks at a time, [anything >2], like with a live band.
BUSS mode recording is more useful when you have multiple inputs, and you want to mix all inputs down to record on one [or two] track, [L/R].
BUSS mode recording will become more important to you, as your production complexity increases.
F/I, you may plug your guitar directly into your mixer Input Channel 1, [LINE IN], and on channel 2, place a mic on the strings, [to capture the sound of the pick on the strings]. In this case, you'd want both the line and mic signal to be mixed, and recorded onto one track. This is when recording BUSS L/R mode is essential, when trying to mix >1 input channel signals together, onto one [or two] tape track.
[in this case] -PAN both Channel 1 and 2 hard LEFT, and record the mixed signal onto either track 1 or 3. PAN both channels hard RIGHT, and record the mixed signal onto either track 2 or 4.
If you leave the PAN in the center while recording in BUSS mode, it's okay, 'cause it will assign the input to the Left and Right, evenly.
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- In BUSS L/R recording mode, the left side of the stereo mix feeds tape tracks 1 & 3, and the right side of the stereo mix feeds tape tracks 2 & 4. This is most useful for complex mixing and signal routing, when recording tracks.
-In DIRECT mode, the individual input goes straight to tape, 1,2,3,4. This is most useful for 4-simultaneous-direct-to-tape, such as taping a live group peformance.
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Both are useful. You can do it any way that works for you.