We actually have an article for this exact question:
https://www.nicehash.com/support/hash-power-marketplace/general-help/why-would-someone-buy-hashing-powerOne of the most frequently asked questions is definitely: "Why would someone buy hashing power?". There are several reasons why people buy hash power at NiceHash, rather than buy the coins directly or buy cloud mining contracts.
*Buyers have done their math, tested different luck factors on pools and reward schemes, and are buying hashing power as an investment to obtain coins at cheaper rates.
*Buyers can buy massive hash power and get it delivered in a short amount of time.
*The order that the buyer places lasts from a few minutes to a maximum of 10 days, which decreases the risk of drastic changes over time in comparison to cloud mining contracts.
*Pool owners buy hash power to increase the luck of their pool or to test the mining performance and compatibility of their pool.