String bending and why its important to do it correctly
Above is a link to an article that talks about the finer details of bending a guitar string in tune. Every players approach to bending strings is slightly different and it takes a large amount of time to be able to do it properly every time.
For me I can always tell a good guitar player from a bad one with the quality of their string bends. This skill in younger players is often overlooked with their focus being on playing fast or chugging along to their favourite nu metal band. A lot of what I see in younger players is they can play fast heavy riffs better than I could when I was their age but then when it comes to the nice melody line they sound like they are strangling a cat.
The skill of having a nice vocal sounding singing bend is something often that is left and overlooked until a later date. All the old great players knew how to make a bend sing just as well as the rest of the notes, bending is a technique very special to the guitar and should be practised and perfected as much as any other skill on the instrument.
Beginner players often suffer with either over bending or under bending or a combination of the two. This will result in out of tune bends and generally make whatever they play sound terrible. Every player has to go through this process of practising the tuning of their bend. Its a battle of two sides, one is your ears and listening for the correct pitch. The other is how the bends feel under your fingers, developing muscle memory for the correct pitch of bends all over the guitar neck. Once you put the two together you will be screaming bends in tune every time.