The practice squad in the National Football League is also known as the scout team, and, indeed, that is its primary function. The 10—formerly eight—players that make up each team’s practice squad serve the purpose of helping the starters to prepare for and scout their upcoming opponents.
This is largely why you see the positional numbers complement what is reflected on the 53-man roster. When there is a dearth of one position on the 53-man roster, you are likely to see the numbers boosted on the practice squad.
When it comes to practice, there is no distinction between a player that is on the 53-man roster and a player that is on the practice squad.