I think the issue is that we don't have meditation teachers. I've had issues with meditation as well, because I didn't know how to deal with certain challenges.

Nowadays, I know how to use meditation as a tool that purely benefits me. I use it sparingly, since I'm a bit lazy. But I've noticed that using it sparingly is erring on the safer side while still getting the benefits.

In my case, I notice the benefits after each session. My mind is calmer and I get less easily upset. In another meditation I'm more empathetic. In another meditation I'm more easily loving.

All effects last for about half a day to a day, but they have ripple effects (i.e. had a good day yesterday? Chances are your day will be great as well today).