They’re opposite. There are A few reasons why this is a good idea. I will state them here. There are few reasons why this is a good idea. This should be stopped immediately. Without the A you’re saying not worth talking about, just move on.

As a native speaker, I'm simply going by what sounds natural to me. I would definitely keep the "a". For example, "There are a few reasons why I prefer to hang my laundry to dry, as opposed to putting my clothes in the dryer. First of all, ..." If I read that sentence without the "a", it wouldn't sound right to me. I hope that helps some :-)

I have 2-3 reasons

"A few reasons why.." is the correct usage here because you are stating a couple of reasons why you think something is a good idea. "Few" is less than "A few" meaning that "A few" holds a greater value or amount or number of things than "few". "Few" : 1 maybe 2 things "A few" : 3 /4 /5 things "Few" : not enough "A few" : enough

I think the others got it. Just to make it simple A few reasons = several reasons Few reasons = not many reasons