My oldest I took once a month till she was about a year, then maybe once or twice after that. She hasn't been officially weighed since her 5 year check was done at school.
My second got weighed on average every couple of months during her first year, but I think I stopped earlier than I did with Chloe. She is now weighed regularly at Great Ormond Street hosp anyway cos she attends there regularly for operations to manage an ongoing medical condition.
My youngest was weighed every week till she was 8 weeks old cos she had trouble regaining her birth weight, but after that I only took her once, when she had her 6-12 month check done at 10 months.
To be honest, I never really had the time with Roxy and don't have any concerns about her development so it wasn't a priority to me. There really is no hard and fast rule and I think it's down to what you feel comfortable with as a parent.