Minecraft wiki entry for Time-saving_tips, associated text: Depending on how you play the game, some Minecraft mods may be ideal for speeding up your work. Tools such as MCEdit, mods such as BuildCraft or Plugins Such as Worldedit provide a wide variety of ways to speed up certain types of routine operation. Not all these mods fit with every playing style, but if you do want to be able to clone buildings, level vast areas, strip-mine to bedrock, and so on, it may well be worth investigating these tools rather than trying to do the work manually.
To improve the game's performance, you may want to consider mods such as Optifine, FastCraft, BetterFPS, or the like. Sodium, Lithium and Phosphor, when used all together can boost fps higher than the previously stated mods. It should be noted, however that they require the fabric loader to function.
VeinMiner can save a lot of time spent looking for ores by allowing you to mine out all blocks of a single type in a preset radius. However, mining in too large of a radius (>1000 blocks) drains hunger and tool durability very quickly and is therefore well used with a tool mod like Tinker's Construct.
For 1.10 players, the Tiny Progressions mod allows for automatic cobblestone creation that costs very few resources and is even better with hoppers as the cobblestone Generator Blocks have very little inventory. You can also place a chest or other storage inventory above the generator and it will automatically dump the cobblestone into it.
To save redstone work in multiplayer, use mods such as Securitycraft and Sticky Redstone.
Many mods add tools or abilities that allow you to harvest entire trees at once.
The infamous Inventory Tweaks mod allows highly configurable auto-sorting of player inventories, chests, and so on, and some tricks to, for example, shift-click one block at a time or automatically replace a tool when it breaks.