armbar question

[Casus Belli]

hey guys i have a question about the armbar. Sometimes when its applied from the bottom i see the person whose applying it reach and grab the back of one of the opponents legs. What is the reasoning behind this? Is it to help you spin or so that the opponent can't stand up?
i think aoki did this against brian lo-a-njoe. Every time i see it i wonder what the exact purpose of it is so any info would be appreciated.

oh and yes i did use the search function.

 

[codemonkey76]

grabbing the leg can help you get the angle necessary, as well as aiding with sweeping them over to their back, making the armbar easier to finish and stop the opponent stacking you

 

[Casus Belli]

Makes sense, thanks

 

[Mikey Triangles]

grabbing the near leg stops your opponent from being able to roll out and escape