Full open "choke" would be 64/64, so the 21/64 choke means that the well is on restricted flow to limit the amount of gas allowed to flow to sales. Think of the well opening as a garden hose attachment that can be open or closed via tightening/closing of the attachment.
WIth current gas prices it would be beneficial to have the choke closed in order to not sell all of your gas at under $4.00 rates. Most current science and well reports also have most of the O&G opperators looking at flowing their wells on a more restricted flow rate as they are reporting that this strategy should extend the long-term life and producing results of the well.
In general, if the operator wants to choke back your well, you're both benefiting from it. He'll cut back production when the gas price is low and you both get more money over time out of the well. The well may also produce more gas over its lifetime at a low flow rate than at a high flow rate.
I say "in general" because there are some conditions where they might be hurting you by choking back your well, but your interests are usually aligned on this.