Talking about aircraft other than FBW Airbus here...
Before takeoff we have set the stab trim for our weight, configuration and CG location. It should be right for the initial takeoff. However, I noticed in lots of swept wing planes that somewhere around 300-500' after liftoff some nose-down trim would be required. A possible explanation for that is that the fuel centroid location assumed in the W&B is based on level pitch attitude. When we go 20-25 degrees nose-up the fuel flows to the aft parts of the tanks including the outboard parts of the wings. This would have the effect of shifting the CG aft slightly.
During and after flap retraction some trim is going to be required.
For landing, it is a technique used by some pilots to trim nose-up throughout the flare and even until the nosewheel touches down. They feel they get smooth touchdowns that way. I choose not to do this normally, and I get about as many greasers as they do. Again, it is a matter of technique and not procedure.
Anyway, when not maneuvering, or, in other words in unaccelerated flight, you trim when you find yourself pulling or pushing against the yoke.
Happiness is not seeing another trite Ste. Maarten photo all week long.