The biggest difference between Hojicha and Sencha is that Hojicha is a roasted version of Bancha or Sencha. Roasting means its process gives extra heat to tea leaves and reduces the amounts of catechin and caffeine. These natural elements are present in Bancha but much higher amounts are found in Sencha.
Catechin is the main natural element of Sencha and this element gives us many health benefits such as effect of anticancer and antivirus, and prevention of food poisoning etc. Since Hojicha does not contain as much catechin as Sencha does, these health benefits are not so much expected as they are with Sencha.
Yet, if you want to avoid caffeine and want to receive such health benefits to some degree, Hojicha is a good tea to drink. On top of it, if you want to drink to relax, Hojicha is the best Japanese tea to drink. This is not just thanks to less caffeine content but also thanks to its distinctive roasting aroma produced by pyrazine. Pyrazine is not present in Sencha but a natural element unique to Hojicha among Japanese teas.