For cruising you likely do not need rachet blocks but they can be handy. In light to moderate air you can just use the block, you do not have to use a winch. The block does not turn back so you have a fair bit of friction when easing the sheet. This allows you to hand hold the line.
I am actually putting a pair on my 30 footer a S2 9.1. Since these boats come with the seconday winches on the cabin top I find that when we are raising or dropping a spinaker at a mark while racing we some times need to hold the sheet or guy by hand for a short period. If it is really blowing that can be difficult. The rachet block would help out here.
I have only had it one one summer so there may be other options but I like the rachet blocks. On smaller boats you can just use them and no winch required.