Growing up, my dad you to stop me mid sentence sometimes and say with his hand raised in the stop position, “No need to say ‘in my opinion’…you are saying it aren’t you?” He was teaching me a lesson that was important. When someone says some statement like “We need to do X” but then follows it up with “…in my opinion,” it drastically devalues what they are trying to say or get across.
The audience or people you are talking to already know that this statement is your opinion. There is not a decent reason to follow your opinions up with “…in my opinion.” It training has helped me in business and in personal situations to be more assertive in how I am presenting my opinions.
A more powerful alternative for “in my opinion” is “my experience says” or “based on my experience”… it is really hard for someone to disagree with your experience.