And by the way, there is a difference between a receiving line and a reception line. The receiving line is formed by the hosts of any event, who will be receiving their guests, and the reception line is formed by the guests who will be going through the receiving line.
If you are hosting a large wedding, it makes sense to form a receiving line so you can greet all your guests at one time and then move on to enjoy the rest of the reception. Otherwise, you will spend much of the time trying to get around to everyone throughout the afternoon or evening to meet and greet them. This can be very difficult to do, and you are more likely to miss meeting some people doing it that way.
Receiving lines at the church can be done well, but you would want to consider the layout of the church. Some churches don't accommodate receiving lines very well due to lack of space. Asking the officiant for advice as to what works best in the church will be helpful. If the receiving line is at the church, your guests can then go on to the reception and start enjoying the festivities. This allows more time for after-ceremony photos for the wedding party.
A receiving line at the reception is typically formed by the bride and groom and their parents. The wedding party is welcome to participate in the receiving line, but it does take longer for the guests to go through it.
Regardless, of whether you have a receiving line or not, your guests should be greeted at some point, by both sets of parents and the bride and groom. This can, of course, be done less formally than a receiving line. Some couples let their parents form the receiving line at the reception while they and the wedding party finish up the photos and then travel as a group in a limo or some other way, to the reception. At the reception, the couple could then work the room or go table to table to meet and greet everyone.