If NXT is switching to Ardor, what is the purpose of holding NXT? There is another snapshot that's happening with NXT for the coin Ignis, but how what's the purpose of Ardor then? So is Ignis the new NXT? Very confused.
If NXT is switching to Ardor, what is the purpose of holding NXT?
Nxt isn't switching to Ardor. It will still exist after Ardor launches. The purpose of holding NXT with this in mind is if you need to use the Nxt blockchain, either for personal use or projects, since one will need NXT for the transaction fees, etc. Another reason could be the speculation of that use, since the amount of NXT in the network is fixed. (I'm not saying one should or shouldn't buy NXT for these reasons. Just pointing out some possible reasons of holding NXT)
There is another snapshot that's happening with NXT for the coin Ignis, but how what's the purpose of Ardor then?
Ignis will be the first child chain on Ardor. Think of Ardor as this giant mechanical robot torso and head. It has everything needed for processing but doesn't really have a lot of features beyond processing, and maybe transferring some data around itself. (There will be almost no features on the Ardor main chain and just the ability to transfer ARDR and forge) Child chains are like the limbs that can be attached to this robot. They can do all the cool things while being powered by the robot torso and head.
With Ardor, there can be multiple child chains. So, if one wants their own blockchain without the problems of having enough nodes, etc., then creating a child chain would be an ideal option. Transaction fees will be paid in the child chain token and not in ARDR, though each child chain will need a bundler in order to collect these fees and pay the main chain in ARDR for processing the bundled transactions.
So is Ignis the new NXT?
Ignis will have a lot of the features on Nxt but will not be the new Nxt. Probably the biggest difference is that all transaction records of Ignis will be pruned after 1440 blocks (~24 hours). Meanwhile, transaction records on Nxt will not be pruned. While there will likely be a archival nodes for Ignis, this might not be desired by some people for their projects, so running it on Nxt would be better. This would also be true if the project doesn't necessarily require all of the features a child chain would bring as creating a child chain won't be cheap. I'm not sure what the price will be yet, but testnet will probably give us a better idea.