I found that the stationary jib blocks on my Oday 23 were perfectly adequate for most sailing conditions with my 100% jib. However, if you race or are a tinkerer, movable sheet blocks are a must.
I now sail with a 135 Genny on roller furling, and I use the moveable blocks further aft. I think they were meant for the spinnaker (which I don't have). I find that I don't move the blocks anyway; I sail in fairly consistent conditions and I find that I'm either single handing and don't have the time to futz with the blocks, or I'm with my wife and guests and I don't have the room or inclination to do so.
Whatever floats your boat....