I'm going to echo a bit of what's been said here already. Italics, bold, and underlining are tools in the same way bullet points are tools. These formats are all useful for:
- Calling attention to specific portions of text
- Adding clarity
- Making text easier to scan
I do not have evidence to say exactly how (or if) use of these tools will affect your rankings, but I'm certain that a user who encounters content that's overly FORMATTED or OneBigBlockParagraphOfText is much more likely to bounce.
So I recommend using those tools to your advantage and writing, always, for a human reader.
