Shravana Mahatmya is performed to seek blessing of Lord Shiva.
None of the day during Shravana Month is Shunya i.e. devoid of fasting. All Tithi during Sawan month are for fasting and perform austerity to please Lord of Destruction i.e. Lord Shiva. Weekdays fasting are also given due importance during this month.
The complete list of festivals falling in the Shravana month is given on this page, including Shravana Shivaratri, Raksha Bandhan, Nag Panchami and Mangala Gauri Vrat, etc. Shravana month is primarily dedicated to the worship of Lord Shiva.
All Mondays or Somwar which fall during Shravana month are considered highly auspicious for fasting to seek blessing of Lord Shiva and known as Shravana Somwar. Most states follow regional calendars due to which dates of Sawan Somwar might differ by 2 weeks.
In North India, Shivaratri which falls during the auspicious month of Shravana is known as Sawan Shivaratri. Except Hindi belt in North India, in rest of India Sawan begins one or two days after Sawan Shivaratri.