Shoelace pose is used within the yin yoga system to externally rotate the hips, stretch the inner thighs and groin and, if you're folding forward, decompress the lower spine.
The primary meridians affected are the Liver, Gallbladder and Kidney channels. If you're folding forward the Urinary Bladder meridian will also be affected.
Yin Yoga Shoelace Pose
You can enter the pose from all 4's or from seated. As you enter the pose press into your hands and rock your weight back into your hips. try to keep your hips even. The tendency is for the top thigh to pull forward. If you have knee or back issues you may want to stay seated upright instead of folding forward. And if your pregnant you don't want to fold forward after about the 1st trimester.
Remember to modify the pose to suit your body and be careful you don't put too much pressure on the knees. If you find it difficult to sit up use height under your hips such as a blanket or bolster. If you have space between the knees place a folded blanket between the knees or under the bottom knee.
A helpful alternative is to do half shoelace with the bottom leg extended. Half shoelace targets the back of the extended leg (hamstring, dorsal chain, Urinary bladder meridian) in addition to targeting the outer hip of the top leg. If you're taking half shoelace you may need to support under the bottom knee to protect against hyper-extension of the leg.
A few more accessible variations to consider are to take "sukhasana" by crossing one shin in front of the other and folding forward from there, or using eye of the needle pose on your back instead.
To release slowly use your hands to guide the legs out in front of you and rest back on your hands. You can also take a counter movement by gentling twisting or doing "windshield wipers".