So much depends on the mix you are using and the target species when it comes to ground baits.
Generally speaking, we riddle in order to put air into the mix which, when made into a ball for throwing, helps the mix break up on the bottom and release the freebies contained therein.
Lumps in ground baits only serve to feed-off some of the fish in your swim which is the exact opposite of what you are trying to achieve . . . . and that is to attract and stimulate but to keep their interest up and not to fill them up. This being one of the major reason why I don't ever use home made ground baits but always opt for the continental mixes in the first place.
There are situations when you don't want the ground bait to break up instantly or over a few minutes, but then there are many ways around that too, and without making a lumpy mix.
One such situation is when I fish for bream on a medium size local club lake. There iy is the kiss of death to keep on feeding as they just don't like to have bait constantly raining down on them, and will quickly go of off the feed.
Simply make, say, 9 tennis size balls, the first three you squeeze just enough to hold it together to be thrown in, the second set of 3 you squeeze a lot harder and the final 3 you squeeze them tightly and then dampen your hands and put a "shim" of water around the outside.
Those 9 balls will then break up at different rates thereby continually attracting but over a much longer period and without having to keep on throwing in more balls.