Mast Bend is a major tool used to control Mainsail Shape & Draft.
The amount of mast
bend depends upon the cut of your mainsail
, your point of sail, and the wind
speeds, and sea conditions ... etc.
More Mast Bend reduces (flattens) the Mainsail, opens the leech, and moves the draft
Less Mast Bend increases draft, and moves it forward.
If your mast is meant to be bent, as a tool for sail trim, it will likely have an adjustable backstay. Masts that are not designed (static backstay) for the use of mast bend, as a tool for sail trim, often have a forward pre-bend.
* Properly using Mast Bend is a fairly technical subject, so I suggest that you Google
< mainsail trim >, < rig tuning >, < mast bend >, and < mast pumping >.