For a +1 to hit:
If you need >21 to hit before the bonus (BTB), it does nothing.
If you need 11 to 20 hit BTB, it gives an additive +5% to hit but does not increase crit chance. Expected damage from the hit increases by .05*(hit damage). This is a multiplicative increase in expected damage between 9% (for 11 to hit BTB including crit on 20) and increasing nonlinearly for harder targets, up to +50% multiplicative damage increase for 20 to hit BTB.
If you need 2 to 10 to hit BTB, it gives and additive +5% to hit and an additive 5% to crit. Expected damage from the hit increases by .1*(hit damage), while possibly also increasing the chance of special rider effects. For an 10 to hit BTB, this is an 18% multiplicative increase in expected damage, while for a 2 to hit BTB it is an 7% multiplicitve increase in expected damage.
If you need a -9 to 1 to hit, it increases crit change by additive +5%, giving .05*(hit damage) extra expected damage per attack and increasing rider chance. Multiplicative increase to damage at 1 BTB is 3% and going down.
The greatest effect of the crit rules change compared to PF1e is in the 2 to 10 BTB hit range: +1 to hit is MUCH more valuable then it used to be. The marginal utility of the +1 jumps considerably if the player can achieve this level of accuracy.