I see it often for safe-checking in alot of scripts but why is it so special? and why do people check for the character model after they check the player is there.
The humanoid is used for a lot of things. A reason why people check to see if their's a Humanoid in something, is so they know it's a player and no tool/hat/part fell and activated it which may cause an error. The humanoid is also used to make a player sit, stand, move to something, and so on. You would also use this with making a status in a player and I believe animations for NPC's. If you didn't notice, the humanoid also causes the player it's inside (Assuming everything is named correctly) to "change", making rounded shapes besides the head. It will also allow character meshes to work, which is how packages work. Also, when this is inside a model with correctly named parts, a health bar and name tag will appear above "Head". There are more things too, but you can do some research on the rest.
So again, it's mainly used to check if a Character has touched or done something, and if this Character is alive.