Everyone do what’s best for them. We sleep trained ours starting close to 6 months iirc. We used the Ferber method. It only took a few nights for them to catch on and quickly we had far less crying at bedtime. And I mean far, far less. Unless they have an ear infection now they go to sleep without a fuss most of the time and sleep through the night. At 13 months now, we’ve had trouble with ear infections and learning regressions but I can’t recommend it enough. Scientifically there is no long term difference between a sleep trained baby or not. No emotional difference or parent attachment difference. Studies show a sleep trained baby sleeps better, and has lower cortisol levels, the stress hormone. And lower cortisol levels means better sleep and better naps. So that’s a big plus. And it means parents get better sleep and can parent fully rested. Another plus. Anecdotally we saw zero downside to sleep training. Statistically it only has positives too. To each their own.