The phrase "small impact" means that something has little to no effect or influence on a situation. It suggests that whatever is happening, the presence or absence of this thing would not make much difference in terms of its outcome.
Sentences with «small impact»
The company that did well would have caused a very small impact on your total investment. (groww.in)
Despite their relatively small impact on your score, too many credit inquiries by creditors can also reduce your credit score. (wisemoneytips.com)
You will have a much smaller impact than you think on motivating them. (inc.com)