Why we shouldn't invest when price dips during XD?

Hi,

I am reading cum-dividend vs ex-dividend at https://www.drwealth.com/cum-dividend-vs-ex-div....

In the article above, it is recommended that we shouldn't invest when price dips during XD. Just wanted to understand why is that so. I am interpreting the concept that it may be make not so much of a difference?

Buy during cum-dividend: Own share at a higher price, but having a dividend.

Buy during ex-dividend: Buy at a lower price.

Both scenarios seems to offset each other.