My current Roll20 Damara 1359 DR campaign is built with a very 1e AD&D feel, so NPC allies & henchmen are common. Currently there are 3 active PC groups:
#1 (5e) currently in the Forge of Fury has 8 PCs level 2-5 & 2 NPCs level 3 & 4.
#2 (5e) currently on downtime has 8 PCs level 3 & 1 NPC level 1.
#3 (PBP, 1e) currently in the dungeon beneath Narcissa's Inn has 4 PCs level 2-4 & 5 NPCs level 2-4.
I tried the Sidekick rules but did not like them, so the 5e NPCs use the PC-class rules now. I found the 5e DMG advice on this works best - use fairly simple PC-class builds for NPCs.
Mostly I run the NPCs but I have started letting a Monk 4 player in group 1 run his NPC Barbarian 4 girlfriend, they have some good banter going on.
This game does not use the Feat or Multiclassing optional rules, which I find helps combat go much faster & enables these larger, 1e-style parties.
I think NPCs in the party are useful for giving the DM a voice, for one thing I can impart information without always saying "Your character knows that...". They tend to strongly encourage In Character play; often with no NPCs present the players default to OOC talk.
Obviously it's important the GM not think in terms of "This is MY character" - no GMPCs as such, though it's ok to be fond of your NPCs as long as you're prepared to kill them should the dice go that way.