Please read the following articles:
Simplest belay device
Inexpensive
Works with 1 or 2 ropes
Straightforward rappelling
Wholly dependent on brake hand when belaying from below; will not provide any braking if rope is dropped
Some models have loop for belaying from above in auto-blocking mode
Interaction between carabiner and device creates extra friction to hold a fall
Can be extremely dependent on device/carabiner/rope combination
Provides protection against loss of control of brake strand
May be less intuitive
Some models can be used to belay from above
Use of various Assisted Braking Tube devices will not be covered in ICS
Many advantages - especially for single-pitch
Can catch climber if belayer is incapacitated
Convenient if partner is “working a route”
Other safety, rescue, and ease of use benefits
A few drawbacks
More complicated to rappel
Single ropes only
Click here for more GriGri Info for Lefties
When climbing multi-pitch routes, after the leader arrives at the top of a pitch they will need to belay the follower(s) from above. There are various ways to belay from above including off the harness directly, off the harness with a redirect to the anchor, and directly off the anchor. ICS will focus on belaying directly off the anchor for the following reasons:
The belay device can be set up to be auto-blocking, which is safer and more convenient
The force of a climber falling does not pull awkwardly on the belayer, possibly compromising their ability to belay
It is easy to escape the belay and help with a rescue if needed
The most notable disadvantage is that it can be more complicated to lower a climber in certain cases.
Another video including some additional concepts
Note: there are better methods for giving slack than the one shown at the end of this video.
If the climber needs to be lowered back down and they are able to unweight the rope by standing up, then the Load Strand Direct method is a simple way to safely lower them long distances.