You might be asking:
1. What should I do/not do with the fairy stones that I have earned?
2. If I cash in to buy some fairy stones, what are the areas I would need to invest on?
3. Where can I get fairy stones?
4. Should I cash in for fairy stones?
Using fairy stones[]
Basically the first 2 questions will lead to the same answer, which is, "which upgrade to prioritize?"
Pet Slot[]
Bigshot Games Developer would encourage you to buy the manager speed upgrade shortly after you receive your 100 fairy stones for answering "Do you like this game". I would suggest that the first upgrade using fairy stones to be prioritized on unlocking the 2nd and 3rd pet slot.
(hint: if you dont have 3 really useful pets or draw the pig - Oink Oink - then the extra slot adds nothing... Even buying the fairies upgrades can help to get coins early after a restart)
I don't know why the previous writer advises to get the 3rd slot... Maybe the prices were cheaper before but right now you should 100% go for only as many slot as you deem truly useful, otherwise get the Manager Speed, it is truly a game changer (as said below, 200% seems good enough, but getting only 100%/150% at first to buy something else before upgrading more is recommended)
Manager Speed[]
After that, you might want to increase your manager's speed since it will improve his speed both passively and actively, which helps a lot if game progression especially towards the middle late game and the late game. I kept my manager speed at 200%/250%-ish as further upgrade would not be worth it.
Fairy upgrades[]
Next up is an optional choice, to upgrade the fairy or not? (fairy upgrade and hire new fairies)
In general, fairy upgrade seems to be more promising than hiring new fairies, but I would suggest to hire new fairies just once (this is to generate gold during stage 1 and straight away upgrading your bag without needing to sell anything).
For fairy upgrade, I am currently at 3x fairy gold, which is good enough for me, further upgrades seemed to be not cost effective, once again, this section is optional.
Resetting accessories repair[]
This would be the end game essential place to spend your fairy stones, each time you repair an accessory, the repair would cost more and more time stones, but with a certain amount of fairy stones (100*number of stars), you can reset the cost of repairing, which saves you a whole lot of time stones, so that you can try to get the best accessory possible.
Do not![]
Get gold is not worth to purchase as the gold obtained caps at 409,000,000
Fairy's Blessing, I would say, don't purchase it unless you wanted to shoot for the max possible rank in boss battle zone.
Raffle, better to spend time stones on this than using fairy stones
Where can I get fairy stones?[]
There are basically 3 ways that you can get fairy stones
1. By purchasing them.
2. By watching an advertisement video (cooldown = 30 minutes of game time). (10 fairy stones)
3. By playing for a certain amount of time (not fixed). (7-15 fairy stones)
Should I cash in?[]
I would say that depends on yourself, if you feel that you wanted to support the developers, then why not?
If you feel that you wanted to play this game free, you can refer to the above section on how to get fairy stones free (item 2 and item 3).