The trolling motor is a brushed DC motor, so I believe there is no change in performance for clockwise vs counterclockwise rotation. The wires are easily reversed on the output of the speed selector switch and the speed resistors are not sensitive to polarity.
The motor may have the same performance in either direction, but the brushes may wear faster in the counter direction.
The 'timing' of the brushes alters with direction and speed, something complex to do with the back emf causing the fields to 'rotate' slightly.
This effect causes arcing of the commutator. The science and the maths behind is complex field theory and I can't actually get my head around it.
If a motor is intended to run primarily in a particular direction at a particular speed they will rotate the brush assembly slightly to the 'neutral timed' point to reduce arcing and brush/commutator wear.
The Perm 132 brushed permanent magnet motor I use in my boat is 'timed' for a certain direction. I actually operate it in reverse. However, I'm using the motor at about half it's rated voltage and power output. The manufacturer actually notes in the manual that if you run the motor on full voltage, it should be run in the correct direction most of the time to minimise brush wear, but that below a certain voltage there is no appreciable difference.
The large motors used in trams and trains have something called 'interpoles' between the field coils, are connected in series with the armature and these interpoles 'correct' the rotation of the field neutral point and keep commutator always in the 'neutral' point. They do this as the motors have to run equally well in both directions and at the power output of these things any arcing is undesirable. The similar (but smaller!) motors used in the air compressors on the same vehicles do not have interpoles, but the brush assembly is rotated slightly to the neutral point for the direction of operation.
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