With final cuts looming, it's the time of year that the practice squad keeps getting suggested as an option for every fringe player who may have potential but isn't ready to contribute right away. And nearly every year there is confusion over just how the practice squad works. It's important to understand that the practice squad is not simply a bunch of extra roster spots that can get a team out of hard personnel decisions.
SB Nation has a writeup on the eligibility rules:
"Eligibility for the practice squad is limited to players who do not have an accrued season in the NFL, or were on an active list... for fewer than nine games during their only accrued seasons. Players that have served two seasons on a practice squad are eligible for a third season only if the team has at least 53 players on its active/inactive list for the duration of that player's employment."
So the gist of it is that anyone with any meaningul NFL experience is ineligible for the practice squad to begin with, especially when you consider that an "accrued season" is only six games. This is a very important point, as fans and even media routinely suggest suggest ineligible players for the practice squad. Last year one of the professional writers even mentioned 11-year veteran Hunter Smith as a practice squad candidate.
But eligibility is just the beginning of the limitations. Even when the guy you want to keep is eligible, you can't simply "put" him on the practice squad.
First, you have to cut him and he goes through the waiver process. Like any other cut, he can be claimed by any other team willing to use an active roster spot for him. This is how the Redskins lost Chase Daniel to the Saints.
If he makes it through waivers, he's a free agent. He's free to turn down a practice squad offer and sign with someone else. For the most part, these sorts of fringe players will just be happy to still have an outside shot at the NFL and will decide their best chance is to stick with the coaching staff that already knows them. It's still their decision, however. When the Redskins tried to sign preseason hero Marcus Mason to their practice squad in 2008 he simply said "no, thanks" and signed onto Baltimore's squad instead because the depth chart there gave him a better chance to see the field.
Also remember that even when a guy is on the practice squad during the season, he is still free to sign with any other team that will clear a spot on their 53 man roster.
The end result is that if the Redskins feel they really couldn't bear to lose a guy, then the practice squad is not an option.