It might depend on how 150mm is designed around the frame and how that affects your riding will depend on lots of other things
how high your BB height will be with the fork at 150mm relative to what the bike is designed around/waht is normal, may sway things as to whether an in between travel would be useful in inbetween situations like twitchy singletrack or techy climbs.
If the BB height were low ebough at 150mm, the 120mm setting could become rarely used
Not talas/2step but my 120-150mm RS U-turns I found I was in the middle all the time on a bike where the upper travel was at the upper height the frame would work with but now they’re on a bike where the 150mm is on the low-side for what the bike will take, I rarely drop below 150mm, only for ‘lay on the floor at the top for a bit’-steep type climbs do I drop to 120mm where the BB height becomes a problem on anything mildy rutted