Roadblocks are still used today in order to slow the enemy on different levels.
On the lowest level you can use a roadblock to slow down the enemy so you can hit him. Say for example you only got light AT-weapons and need to fire on a road. hitting a vehicle moving 40-50km/h on 100-200m distance take some skills, and with heart racing, combat around etc it becomes even harder. Putting up a road block behind a bend or whatever either halts the enemy or slows them down to make the shots easier.
You talk about moving the obstacles really quickly. well it might look that way, but dig down 1-2 mines in that road block and see how fast it takes to remove it after the first mine detonates.
Obstacles and mines are "normally" defended, which means that when a enemy encounter a minefield or obstacle they deploy for combat, and moves slower untill they know there is nothing. this takes time, and thereby buys you time. That also makes them much more accesible for indirect fires, a FOO and a bunch of roadblocks can pin down the enemy for a good while for example.
On a bigger level many roadblocks can either slow enemys advance to buy your side time to do a propper defence or make the enemy accesible for a counter attack and so on.
Roadblocks are a very useful weapon in the way i have described and its particuly so when you look at the time it takes to make. Ad hoc roadblocks can take just about 5 mins (driving out some trucks in the road, throw a visible mine infront of it) or just a few hours work (saw or detonate trees accross the road, blow up the road etc and depending on what you go for it doesnt have to be manpower heavy either.
I am a combat engineer in the swedish army and we have plenty of heavy forest to use and canalising terrain so we use roadblocks ALLOT mixed with mines and proper minefields to delay the enemy, to make them change direction (into prepared better defences) or to hold them where they can be counter-attacked, so its a great tool really.