Hi @Elisa147 You don't have to approve or decline, but you do have to respond. It's your response rate that is considered. I don't pre-approve every inquiry, and I decline very few, but I do answer every single inquiry as quickly as I can.
It's up to you if you want to pre-approve. All that a pre-approval means is that you have locked in the price for that booking for that guest, for 24 hours. Once you have pre-approved a guest, they can book directly without further conversation with you.
Your calendar is still open, you can still take other inquiries, and you can pre-approve more than one guest for the same period. First come, first served.
Unless you think the guest will be a problem, it's really no big deal to pre-approve, but again, it's not necessary. If you don't pre-approve, and they want to book, they will simply submit a reservation request. If you get an actual reservation request, then you must be careful, as now a decline WILL hurt you. So to be clear, a pre-approval is completely different than a reservation request, and the consequences of your actions are different as well.
Good luck to you.