Sniper's high burst damage is useful in the early-game, while serving as okay damage towards the mid-game. Use it to pop high-HP Bloons, especially the Blooming Bloon (which can be one-shot outside of Dark Castle). However, many other options deal higher DPT for lower cost, including Bomb Shooter, Mortar Monkey, and Dart Monkey Twins.
Compared to the Bomb Shooter, which costs 1 less Gold and has Armor Piercing, the Sniper has one less reload and counts as a Military Monkey (mainly impactful for War Bonds).
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.
The Leeching Shot Sniper, despite being an Uncommon instead of Common, has more utility than the extra damage per shot offered by the ordinary Sniper.