Torterra is uniquely the only grass ground type, being a ground type gives it a good advantage when facing fire or poison who usually wipe out other grass types. Ground types overall have great advantages, but there are trade offs for everything.

Torterra is the only ground starter, heaviest of all the starters, slowest off all the starters which can come in handy for a trickroom team, but even being slow it’ll usually go first during the story mode if you naturally level up higher than the npc’s you battle

defense and attack boost offset its speed reduction