What does "against the Sunnah" entail?

Assalamu Alaikum,

I always see this answer whenever a caller asks the sheikh about a specific thing to do or not to do. The sheikh sometimes answers with "it's against the Sunnah" but not whether its haram or halal. I say this because a lot of things are considered Sunnah but are optional. So when they say "it's against the Sunnah" do they mean that it is optional to do or not (obviously better to not) or do they mean that it is Haram. For example, someone asked about the beard topic years ago, the sheikh said its against the sunnah to shave, but I have an issue where my skin is sensitive so a beard causes me rashes and bumps on my skin so I shave it out of discomfort.

Thank you brothers/sisters