Bhrigu Express: बलिया की आन बान और शान , भृगु एक्सप्रेस है तुम्हारा नाम। हर रविवार तुमसे मिलना है मेरा काम। - Shanzil Kabir

My Guess - Magadh 12401 / 12402 rake sharing with Shram Shakti 12451 / 12452 done for -
1. Magadh will be an NCR / CNB base train.
2. NDLS won't do primary maintenance of 12401.
3. 12401 will run on priority in NCR / ALD, as NDLS need to do secondary maintenance and depart 12452 from NDLS at right time.
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This RSA will save 1 rake and with 4 rakes, these 2 trains will run on time.
5. This won't require any time table change for both the trains.
6. Magadhs' 75% run is on NCR, so this will automatically set the precedence for Magagh to run good in NCR :)