What should be the best practice in responding to Outlook Meeting requests? Do organizers like receiving emails that their request is accepted? Do we all truly understand what happens when we send each response?

The first two options (Edit the response before sending & Send the response now) both send an email to the organizer, and the attendee's response is recorded in the organizer's tracking list.

The third option (Do not send a response) does not notify organizer, so the attendee's response remains as "None" in the organizer's tracking list.

By default, Outlook only updates the meeting tracking when a respond is sent.  If you accept a meeting request and select the 'do not send a response' option, it will add it to your calendar as attending but it does not update the organizer's meeting tracking list.  The response will be shown as none.  Many people choose this option so that the organizer email is not overrun with these responses. 

However,  Microsoft may change this feature in the near future

Many users report that they expect Do not send a response to be recorded in the organizer's tracking list, but just not to send an email. Microsoft is considering updating the behavior so that all 3 response options are recorded in the organizer's tracking list. Attendees can still use the Do not send a response option to avoid sending email to the organizer, but their response would now be recorded & shared with organizer.

To let your opinion be know on the change, visit: https://techcommunity.microsoft.com/t5/office-365-calendar/accept-amp-do-not-send-a-response/m-p/152153

When the organizer sets the meeting, they can also choose a separate option to not require a response and if the organizer does not require a response, the meeting request should have its request responses disabled so no choice is available to attendees.