These things are basically usable for everything. They do huge amounts of damage, as their main attack hits twice. They gather basically everything. They are decently quick, have good stamina. They have decent health, can damage stone structures, and one of their attacks can hit riders.
However, their weight sucks. If you are using this for gathering, pump just weight and maybe a bit of melee.
To get wood, use normal attack which is slashing with claws. To get berries, use bite attack. To use bite attack on mobile, change multi tap to alt attack 2 and tap with 2 fingers when riding the Therizinosaur. To get fiber, use the tickle with claws move. To use the tickle with claws move on mobile, jump when riding the Therizinosaur.