It's really simple... It means something exceeds in certain quality by a little bit. You can roughly translate it to "a little too <em>adjective</em>" or "a little <em>adjective</em>-er than it used to be"

This examine is a little harder <em>than it used to be</em>

這次考試<em>比以前</em>難了一點

His criticism is a little too harsh

他的批評狠了一點

Or you can simple rephrase it “...了一點” = “比較...”

这个语法难<s>了一点儿</s> = 這個語法<em>比較</em>難

这次考试的语法有点儿难! ( subjective)

这次考试的语法难了一点儿。( more difficult than a standards, the norms, compared perhaps with the similar exams before etc.)

You can review the grammar point- the difference between "有点儿" 和"一点儿"