The Rebbe stated that (minimally) one should immerse in the mikveh on days when Tachanun is not said.
(Sichos ha-Ran 185)
Reb Noson discusses the importance of heeding Takanas Ezra by immersing in the mikveh prior to davenning after one has experienced a seminal emission on the previous night. Although this is not halachically required, Chassidim and anshei ma’aseh are careful to do so.
(See Likkutei Halakhos, Hekhsher Kelim 4:16. When a mikveh is unavailable, showering under a total of nine kabim of water removes tumas keri. This usually takes about five minutes standing under the water.)