There are many reasons why someone would want to use lubricant during intercourse.

Hormone fluctuations during pregnancy, after delivery, and while pumping or breastfeeding can make things a little drier, even if you are mentally and emotionally ready to go. (Although vaginal dryness is very common, pain with intercourse is not and could be a sign that you would benefit from an evaluation by a pelvic floor PT).

Hormone fluctuations during menopause can make things a little drier as well. Vaginal dryness can occur for a number of reasons, including the aforementioned. Using a lubricant can also reduce tissue irritation and tearing. It can also just make sex more pleasurable.