Sniper's high burst damage is useful in the early-game, while serving burst damage towards the mid-game. Use it to pop high-HP Bloons, especially the Blooming Bloon. Notably, it can one-shot a Blooming Bloon except if buffed by the passives of Amelia or Zee Jay. It has greater damage-to-gold ratio to single targets than most early-game Monkeys.
Compared to the Bomb Shooter, which costs 1 less Gold and has Armor Piercing, the Sniper has one less reload, has 10 extra ATK, and counts as a Military Monkey (mainly impactful for War Bonds).
Night Vision Sniper costs 1 Gold more with 10 extra ATK than the normal Sniper. In Striker Jones decks, having both of these Snipers is useful to survive early-game more consistently.
While a decent candidate for Try this!, and serviceable in newbie decks, most other Monkeys are preferred for the early-game once unlocked. As a Common, however, the Sniper can be drawn more likely than more popular early-game cards such as Barrel of Monkeys.