BY
Worth 7 points before any premium square, and the 7th highest-scoring of 96 — tied with 2 others.
BY extends into 3 three-letter words, which is the 8th least extendable of 96. That is the number worth memorising: a two-letter word is a place to put tiles, but a well-hooked one is a place to put them where the board stays open.
Every hook
- A→ABY
- E→BYE
- S→BYS
Not all of them are equally reachable, which a bare count of 3 hides. BY hooks on 3 distinct letters, and the ones you are likeliest to be holding are E (60% of opening racks), A (49% of opening racks) and S (26% of opening racks). The rarest is S, at 26%.
How often you can actually play it
Out of an opening rack, 1.61% of the time you hold the letters for BY outright, the 5th least likely of 96 — tied with 2 others. Counting a blank as whichever letter is missing lifts that to 4.85%, though spending one of the two blanks on a two-letter word is rarely the play. Exact hypergeometrics over the 100-tile bag, not a simulation.