I have helped do it on a relatively large HO layout for a friend's club (he was the track maven). Advantages? For one thing, looks realistic since you are spiking down the track with spikes, like the prototype. You also can choose the rail code/size you use, and the ties. And because it is handlaid, it looks like the 'real thing' since it is usually laid by people and you get natural variance (ties not perfectly aligned, the way the spikes are) (I realize that it has changed with things like pre done sectional track in the prototype or using concrete ties).
People also lay it different ways. Some make the track in a jig, where the ties lie in depresssions, the track is aligned by the jig as well, and you then spike it (kadee used to have a stapler like thing that spiked both side of the rail at once; cheating according to my friend).
Others glue the ties to the roadbed, then they had a jig that held the rails at the right gauge, and spiked it. another method I saw was where over a length of the track to be, they marked the lines for the rail on the tie surface, then spiked the rail to cover that line. They still had to align the second rail laid, make sure it was in gauge. Curves are similar, with a jig it is a lot easier then gluing down the ties then spiking IMO.
As far as turnouts go, to me not worth the effort (my friend would grumble that I am just lazy; on the other hand, he has done so many it probably is easy for him). If I was going to hand lay (thought of doing it with my three rail layout, decided that Ross looked great) I would do the track and buy switches.
