The usage of 有 in comparisons
When use 有 in comparison: 

In positive way you can use 今天和昨天一样热(Today is as hot as yesterday) or 今天有昨天那么热 instead of 今天有昨天热.Because it's more normal expression.

In negative way you can use 他没(有)你(那么)细心 which will omit character 有 or 今天没(有)昨天(那么)热.

It's better to add 那么 in comparison to emphasize comparison.