hanamaru
List several reasons or qualities
〜し lists several reasons or qualities together, like 'and what's more'.
JLPTN5
... し、... し~ shi, ~ shi, (~)
[reason/quality], and [reason/quality], and so on
Attach し after a plain-form verb, adjective, or です/だ to pile up reasons or features, suggesting there are more besides the ones you name. It often implies that the listed points add up to a conclusion. Listing two or more with し sounds more emphatic than just stating one reason.
Tips and Common Traps
Hana· Key point
し is great for persuading or recommending — when you want to say 'it's good because X, and Y, and there's more!' It gives your reasons weight.
Maru· Common trap
With な-adjectives and nouns, drop な and use だし: 便利だし (it's convenient and...). Don't leave な before し.