I don't get it why people are always so afraid to do things on their own.
But, regarding to semi-solo hiking. On long distance trails like the PCT, couples often hike separate so each can hike at their own pace. Especially when there is a lot of climbing/ decending involved, because that can be very tiring if you cannot hike at your own pace. Then they meet at water sources, mountain pass or other points where they have agreed to meet. Of course when things get technical/ dangerous then they would stick together.