If you have a windscreen for your standard cam mic (for example XL1S) can you always leave it on the mic?
I did a search and I couldn't find a conclusive answer, although somebody asked something similar.
But what's the result of leaving the windscreen on the mic indoors? Does the dialog come out better, or does it have a reverse effect indoors, and it has a worse sound?

Thanks,

Since the xl series stock mic picks up everything indoors due to it's broad cardioid pattern the best thing to do is remove it from the camera indoors along with the sock. Or just switch to audio1 in.
You did say dialogue in your post, so to do this, external lavs in combination with directional mic(s) are the way to go.
You can use the on board mic, but since the near field room presence is very "alive", sock or no sock won't make any difference.

We never remove them...for any reason.

RB

Most stock foam windscreens create a very small reduction in high-frequency response. Under most conditions indoors or outdoors with a stock mic, this will be an insignificant difference.
I'd leave it on to prevent noises caused by drafts, or moving the camera around.