/gmroll is most commonly used for the GM to make private rolls (things happening outside of the PC's awareness, and in some cases player rolls for stealth or perception so that players don't know how well they rolled outside of the GM's description of the result, though this is not universal), though it can be used for situations where there is a need for a player's roll to be kept private - such as PvP actions (one PC is pick-pocketing another PC) or the party is split and it is desired to keep their activities hidden from the other players. But during normal play, for most gaming systems (D&D 5E included), player rolls are usually made publicly.

Just look at the analog P&P experience, where only the GM has a privacy screen. In this scenario the players really have no easy way of making private rolls, and the flow of the game reflects this.

/gmroll is most commonly used for the GM to make private rolls. This could be for things happening outside of the PC's awareness such as NPCs setting up an ambush, random encounters, etc. In some cases, player rolls for stealth or perception might be made by the GM so that players don't know how well they rolled outside until the GM describes the result (this can often be used to prevent meta-gaming, but can also increase the suspense and immersion), though this is likely more rare than allowing the characters to make their own rolls in these circumstances.

It can be used for situations where there is a need for a player's roll to be kept private - such as PvP actions (one PC is pick-pocketing another PC) or when the party is split and it is desired to keep their activities hidden from the other players. But during normal play, for most gaming systems (D&D 5E included), player rolls are usually made publicly.

Just look at the analog P&P experience, where only the GM has a privacy screen. In this scenario the players really have no easy way of making private rolls, and the flow of the game, even when transitioned to online tools, reflects this.