Everyone has his own opinion about drones and it all doesn't rly matter if you think about it. The whole liking or not just has to do with the use of drones and battletactics.
Here is how I use drones.
A drones, use em as shield. Yeah the marginal firepower they have rly is pathetic, however I do use their wound to save crisis of broaside suits. Whether the guns kill something doesn't even matter to me; I just use them to die for the greater good. Instead of losing a stealth I lose a drone...I always take 2 drones with my stealth too.
Basicly they're just weaker shield drones.
Real shield drones are used for the same purposes but on more espensive chars, which I don't want to loose and have an extra backup.
I ususally give 2 drones at max to a squad, but I'm thinking about going to 4 or 6 in bigger battles to increase their odds of surviving.
I keep marker drones for pathfinders or firewarrriors. They're expensive, but having that markerlight is great and it remains on the battlefield during pretty long. I use every markerlight I have and rly lov using them, I only regret the expensiveness of these drones, but then again it does give an extra wound too, unlike having the markerlight on the shas'ui. I rly like the fact that you can have more than one markerlight in a firewarriorsquad now. Back in the beginning of the tau I used to take squads of 6 with a shas ui to have 2 markerlights...I still do it at times, cuz I don't have many marker drones.
I do give A drones to firewarriors squads of pathfinders to increase their survival in cases I need to stay in some big important spot. I do this very rarely as the max number or firewarriors already takes care of this in a way.
In the end they're all pretty cheap and A drones and cheap canonfodder (for a tau army) They're rly good canon fodder too! At times both A drones and shield drones work as excellent shielding drones as they survive through mutiple shooting (especially the shield drones). they're both great if you're in cc by mistake. You increase chances of escaping by putting them in front and dieing for you. I rly have to admit that at times they have amazed me and saved me from the worst situations ever, especially against cc lol. They may be canon fodder, but their save is far from being that bad. Imagine a lascanon shooting at your crisis...drone dies...crisis are ok...or Shield drone survives and it was nothing! even better!
It has been worth it in the few situations I've used them.
Drone squads and drones from piranhas or devilfishes are used in the same way, except that they're not in the squad which is even better :p.
As for tactics...
I make sure that my crisis suits don't get shot at a that much...this makes them benefit from their extra wound even more as they could prob just lose the drones, instead of a suit or 2.
I have to admit that at times they server as great last resort (against cc mostly) but most of the time they're just there to minimise death within squads. This whole tactic is great to preserve your units intact (I don't consider the drones as part of the squad, they don't do much anyways except to die for the greater good, more important is the shooting from the crisis suits which I want to preserve)
Another big reason why I can afford them: most times I have all I new and have "points leftovers" they fill the wounds of the squads greatly!
I agree with Andromidius completely, I prob use the stealth in the same way and it works great...that great I prob use it in every battle.
Now 2 squads are completely different, broadsides and my HQ crisis team.
Broadsides don't need shielddrones however it could be a good idea to give them that extra 2 "super" wounds. I give me invuln save at times to increase their survival if rly rly needed. I give em shield drones if I know I will suffer dam, but have to stay in a spot as long as possible and even if I may lose the whole squad, having them untill the end will be worth it for sure.
Rly is a final resort, usually don't do this, as it's kinda useless. Adding 2 or 4 a drones is nice to have extra backup. I don't do this unless I have tons of pointsleftovers.
SHield drones on the HQ criss team, now that different. Both they and the etheral are valuable units for sure, I don't regret one bit addind these to them.
They do great during battles and asorb rly anoying heavy shots. (don't you just hate it when you crisis suit dies from insta death , while in my case just one drone may die, but he may even survive lol :p)
At first I didn't apply all these tactics, but then after years of playing I realised that at times I did take extra units for nothing (at end of the battle they had barely done anything and had prob stayed intact), while I always hoped the units I was using would survive longer...drones helped me with that :p
This still happens to me with other armies lol.