I asked this question about my Ti frame and the builders (Enigma in the UK) recommended the slot in the frame and the clamp aligning to avoid galling.
I have flipped my collar 180 degrees so itâs not aligned with the frame slot, reverted back to the original position, and then flipped it yet again as this thread has progressed. I think I need to unsubscribe and go for a ride.
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I think bar tape direction does matter 
Wrap direction is meant to help keep the tape tight when pressure is applied, usually to the outside of the drops. Otherwise you may âunwindâ the tape inadvertently. Maybe this will become a new thread!
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Youâre more than welcome to start that thread 
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I am used to having the slot of the frame align with the collar slot. Both at the rear. Ti, steel and aluminum frames. However I was recently dealing with a Caad12 and the collar had a notch opposite the bolt clamp so the bolt was to the front and the frame slot behind, with the notch in it to align it.
Maybe it depends on frame material?
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Recently fitted a lightweight carbon post and instructions said the same thing - collar gap should be opposite side to seat tube gap.
Instructions seemed to suggest that aligning with slot increases chance of the seat tube biting into the carbon post.
This is also new to me, but then being the kind of bloke that likes to just figure stuff out, I rarely read instructions. With advancing age comes advancing wisdom, and so Iâm now reading instructions more often than not, and finding that seat collar alignment is just one of many things I was getting wrong.
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^ This.
The only problem Iâve seen myself is a steel frame biting a gouge into an aluminium alloy seatpost: unfortunately for me that was a C record post. Ouch.
FWIW my solution to the problem is not to slot the seat tube: all my seat tubes are a full circle at the top so collar orientation doesnât matter. Easy to do by manipulating fibre direction in composites, donât think it will work in metal.
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I have a bike/seatpost/seatclamp combo that only works when the gap in clamp is aligned with slot in seattube. In other position seatpost will easily rotate even when seatclamp is properly torqued. The problem started when I switched the heavy seatclamp to lightweight one.
You can also add OneUp V3 dropper post to the listâŚ