Shukla Chaturthi is the name for the 4th Tithi (lunar day). It's nature is Khala Prada,
which can be interpreted as "cruel, wicked or bad in nature". It's good
for using weapons, keeping arms, killing of enemies, arresting actions,
poisoning, igniting fire, Atharva Vidya, works related to electricity. No Manglik (auspicious) works should be done as they get destroyed.
Ganesha (Ganapati) is Devata which rules the 4th Tithi (referring to Muhurta Chintamani and Poorva Kalamrita), which is good for the destruction of one's enemies, the removal of obstacles and acts of combat. As per Brihat Samhita, Shukla Chaturthi is ruled by Yama and all actions done in respect of Yama are acceptable.
Being Rikta (that can be translated as "empty hands", "scanty", "destitute") and ruled by Shani (Saturn), 4th Tithi is
suitable for following works: arresting, poisoning, uses of weapon,
surgery, igniting fire. Travelling in any direction is strictly
prohibited during Shukla Chaturthi.
During the vedic month Magha Shukla Chaturthi becomes Sompad Tithi, which is considered auspicious (Sompad Tithi is connected to Soma, which is a keeper of Amrta, divine Devata nectar of eternal youth).
During the vedic month Pausha Shukla Chaturthi becomes Maasa Shunya Tithi, which is considered inauspicious in succeeding in works started during this Tithi.
Shukla Chaturthi becomes Daghda Tithi (burned lunar day) for times when Surya (Sun) goes through Vrishabha (Taurus) or Kumbha (Aquarius). It's considered that Daghda Tithis are inauspicious to start any type of work.