If you get an opportunity to choose a new ability when you level, do you lose it if you don’t use it before you level again in Diablo 3? Or can you save those ability choices up so you can e.g only start using some of them when you’re level 50 or higher and better ones are unlocked?
You can use them straight away, but you don’t have to, and they are not lost. Sometimes (often) the new skills and new skill runes that become available are of no use or worse than those already unlocked. At level 70 all skills and passives are available. Remember to go into options and choose “elective mode” so that you can use several skills from the same category.
Also they are not exactly “points”. At level 70 you start to earn paragon points - which is another subject. 