New Player

If for no other reason, NPCs are valuable in that Elmo does a great impression of Fruella. Of course, you have to have them both in your party at the time.

With a party of five, you won't encounter much full time need from NPCs, but they can be used situationally.

For example:
I like to take Burne along with me to hunt the Gar, so I get an extra fireball/haste caster.

I like to grab Elmo in the beginning for Deklo camping or the surface of the moathouse. I usually drop him after my characters hit level 2.

I usually take Otis to help me with the first level of the Temple (clearing out the non-temple related monsters). After that, I can usually handle what's coming.

The evil NPCs are very useful too, but hard to roleplay unless, of course, you have an evil party.

All in all, unless you are playing just one or two PCs, the NPCs wont cover anything you don't already have.

I found that a fun and challenging way to play is to create just one PC (your choice) and round your party out with the appropriate NPCs. IMO, it's the closest thing you'll get to PnP D&D where you can't really control the other members of your party, even as the party leader.

 

...which is, if I may jump in awkwardly, probably why it's more appealing to someone with a PnP background. Personally, I have almost no PnP experience, and I became interested in the ToEE precisely because it allows a full party of PCs like the Baldur's Gate series. I stopped playing Neverwinter Nights and instead began to play the ToEE for this reason.