I usually like to ride alone because my schedule is so funky. I can go ride on a moments notice. I've done group rides and they are a blast. I talked to one guy (retired) who said he use to do 90% of his rides solo and 10% group he now says it is the opposite. Even if you only do a group ride once in awhile it can motivate you on your solo rides.
The cons are you are tied to other peoples pace and breaks. As you mention the drive time sometimes you can be done with a ride by the time you drive back and forth to a start location.
One other plus I didn't see mentioned is you can learn new routes that you can do solo later.
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"I've been dropped a lot of times, but it's never been because of my bike." DXchulo