Use of pronoun "en"

Question

Is the use of "en" is necessary in the following phrase: "j'ai pu rapidement en constater les effets sur ma facture d'électricité."

Accepted Answer

Bonjour James,
Indeed ‘en’ is required here, otherwise the person you are talking to won’t be sure of which effects you are referring to (‘d’éteindre systématiquement’).

- J’ai pris l’habitude d’éteindre la lumière. J’en ai constaté les effets.
I took the habit of swtiching off the light. I noticed its effects.
- Tu as besoin de partir en congés ? Oui, j’en ai vraiment besoin.
Do you need to take some time off? Yes, I really need it.

See link here: the-adverbial-pronoun-en-can-replace-a-phrase-introduced-by-de
I hope this is helpful.
Bonne journée !