Skims are useful for saving time for making T-Spin Triple layouts. Although they break back to back, they do add firepower in case you can't stack for one!
Grim Grotto: Slotting in an S/Z into a 2-wide hole horizontally will replace the row with a 1 wide hole. This proves to be useful in building TST notches.
Super Grim Double: This is important for making STSD, take note! So now 3-height 2wide holes are now easy pickings for STSD!
Make sure the vicinity the S/Z is pointing at is clear before you do this, otherwise you can't fit the T in!
If you create a 2 wide well above a TSD, you can skim into a Trinity!
You would be surprised how frequently this happens..