“While balancing taps and sinks is key for keeping a game economy balanced in an instant, understanding which sinks are actually sponges and how long it will take to saturate them is key for long term viability of both minimizing inflation and keeping room for long term player motivation. […] In order to design BitCraft as a true sandbox game that won’t exhaust its content we take care to consider which aspects of the game are true sinks and which are sponges. This concept can extend even beyond the game’s economy to the balancing of how a player can spend time playing. For example in most MMORPGs, leveling up your character or gaining more powerful equipment is a sponge for your time in the game. Eventually you can reach maximum level or gain the ‘best in slot’ equipment and this sponge will be completely saturated, with the player losing motivation to play. This is why you’ll often find games design these sponges to saturate with diminishing returns to try to make sure they never fully saturate or wring out the sponges periodically with a soft reset (level cap increase, item power creep, etc).”
Content retrieved from: https://massivelyop.com/2023/10/31/maxing-all-of-mmo-sandbox-bitcrafts-core-progression-skills-will-take-a-player-years/.