The benefits of donating blood 400ml are boosting metabolism. The disadvantages of donating blood 400 are that it can cause fainting and infection. 1. Benefits of donating blood 400 Promote metabolism: After donating 400ml of blood, it can promote hematopoietic function to produce blood cells and generate new blood cells. 2. Disadvantages of donating blood 400 (1) Fainting: For first time blood donors, fainting can be caused by nervousness. (2) Infection: If disinfection is not in place or irregular blood donation procedures, it can lead to infection of other diseases, such as AIDS, Hepatitis B and so on. You must go to a regular hospital or a regular blood donation station to donate blood, and donate blood appropriately according to your own physical condition.