Some academies look down upon beginners training leg locks. This is because certain leg locks (heel hooks in particular) can cause damage much faster than a normal submission. Most beginners will crank the heel hook a little too hard and the person getting submitted won't even feel the pain until it is too late.
This is fine if you are simply training for your own skill level in the gi. However certain tournaments allow leg locks in no gi very early on in skill level.
To ease into it, I believe they can slowly be drilled to feel out the pain thresh-hold and can be applied SOFTLY during rolling. There should be a mutual understanding between training partners where you know that the person who is applying it is not doing it full force.
And tapping early to the leg locks in training at least is encouraged (until you get more advanced).
Now another slick submission by Davi Ramos