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For the most part, the ride skill is a hook that builders can use or ignore when they set up their mods. Most ignore it, honestly.
It was meant to allow mounted combat and to affect both the PCs combat ability and, if I remember right, concentration checks for casting spells.
Certain prestige classes have a requirement of a certain ride skill (usually only 1 point, I think), but otherwise make poor use of it.
As Henesua says, it's really up to the builder how to use it and how important to make it. Like Persuade and Intimidate. Some of the best mods, IMO, make exceptional use of these skills. Most don't.
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