I play Shadowrun Dragonfall Directors Cut.

Do I need throwing weapons to use grenades effectively?

Throwing Weapons improves a character's accuracy when throwing grenades.
Reaching level 5 in Throwing Weapons will also reduce the AP cost of throwing a grenade to 1 action point (instead of 2).

Thanks! I appreciate your help.

Grenade accuracy will always be high, so the skill is not required for hitting.

However: To throw grenades for 2 AP is not that effective, so if you plan on making grenades your thing you'd still need throwing 5. Knives / Shuriken need high Strength to be effective, but if you have that they are very powerful and could be used as a main weapon. One of few ways to effectively combine melee & ranged btw. It's even better in SR: Hong Kong, but it already works in Dragonfall (if as an exotic option).

Yes.

Also, better strength grants the ability to throw them further.