You're correct. You can't dilute it by adding anything to the pool. However if you also increase the amount of entropy that the system thinks is in the pool this can cause issues. The system keeps a log of the amount of entropy that it thinks the pool has. This is reduced when in some cases for example when urandom is used. When the entropy remaining runs out urandom will have to wait for more. You can specifically tell the system "I've added lots of entropy" and then urandom will not stall but may make some not-very-random random numbers. So adding to the pool is a good thing but don't tell the system it has more entropy and don't expect to get random numbers faster.