Bagpuss said:
Closer to the truth is they keep them at max ranks or 5 ranks for the synergy bonuses or Prestige class requirements.
Quite true, in my experience, PC's put ranks in skills for one of a handful of reasons.
1. It's a skill key to their character concept (like Pilot for a starfighter ace, or Diplomacy for a negotiator-oriented Jedi Consular), and they not only max it out, they do every trick they can to get Synergy bonuses, take feats to boost the skills, and go for PrC's and class abilities that augment the skill or take advantage of it.
2. They max them out if they are a class skill, as it's something useful and it makes sense for the character, and they've got the points to do it.
3. They get enough ranks in a skill to meet a PrC requirement (or a feat requirement or some other reason to take the skill), but don't take more ranks unless it's really needed.
4. They get a rank in it so they can use a Trained Only skill, and get enough synergy and ability score bonuses, and maybe an extra rank or two, to perform a few common tasks they want to do with that skill.
5. They start with a few ranks in them as a background/character concept thing, maybe for roleplaying, but never raise it past there.