Factor Shifting is vital early-game as it reduces your Base by 1 (outside of Challenges), and the Base significantly affects your Ordinal and thus, OP gain to go with it. It also unlocks a new Factor which allows for more multiplicatively stacking benefits to Tier 1 Automation's efficiency.
Additionally, Factor Shifting resets everything that precedes it, restarting the features that performing a Markup normally does, and resetting your Factors and Ordinal Points. You can only perform 7 Factor Shifts per run outside of Challenges, as having 8 Factor Shifts would drop the Base to 2 and break the game.
Factor Shift 8 can only appear before the first Factor Boost you will ever perform, and is a disguise of the first Factor Boost. Factor Shift 8 does not show up if you have performed a Collapse before, since you should have already Factor Boosted before. All Factor Shift costs here are rounded to the nearest integer.
The lowest currently possible Factor Shift requirement is 3; it is only possible for the 1st (with at least 3.229 OC4 completions) and possibly the 4th Factor Shift (with SFU73 and at least 4.095 OC4 completions).
To reduce the FS1 cost to 1 OP, you need around 13.067 OC4 completions.
According the doc for OM:Rewritten, there will be a change in Factor Shift costs; most of them are cheaper than original version. (200/800/3000/50000/2e11/3e20/1e100)
According the doc for OM:Rewritten, every time you Factor Shift, they will increase the base of Factor 1-[Factor Shifts-1] by 0.1.
↑This is actually Factor Boost 1, if you’ve never done one before.