It’s a little hard to answer this question definitively, but typically, adding semantic markup can benefit SEO (because robots understand what they’re parsing better) and can benefit end users (because their various technologies, which could include screen readers among many others, also understand what they’re parsing better).
Search engines and screen readers also often present things back to users in more easily scannable formats – for example, using a real <ul> instead of pasted bullet characters enables screen reader users to hear “List with 17 items” instead of just “Bullet text of list item one.”
If Google is the primary search engine you’re interested in affecting, you can use their various tools – one of which is the Schema Testing Tool – to determine what structured and semantic data may be of use for your site and may enable Google to display richer search results, which can increase clickthrough rates.