For the 1X conversion of my Trek FX 2, I replaced the stock 8 speed 11-32 CS-HG31 cassette with a 8 speed 11-30 CS-HG51 cassette to (1) fine tune my gear range and gaps and (2) have shiny silver drivetrain.

Why not go 1x10 if I was willing to buy a new cassette? Because the Trek FX 2, like the Scott Metrix 40 (Scott Metrix 40 Bike - 2014 | REI Co-op), comes with Shimano ST-EF51 integrated shifters (i.e., with built-in brake levers) which are limited to 8 speeds. So going from 1x8 to 1x10 would have further required replacing (1) rear derailleur, (2) shifter, (3) shifter cable, (4) pair of brake levers, and (5) pair of brake cables. Way too much expense and effort for a casual bike.