Check them at the first service, then it should be a part of any major service. If you just have to tighten spoke or two slightly it won't make enough difference to notice, but it will change how tru the rim is. Spin the wheel with a pointer close to the rim, a wrench screwdriver just anything to gauge with. That should let you know if it needs to be trued. Don't go by the tire, they almost all have a little wobble.