People who are familiar with bitcoin core will know that it has a console command call 'prioritisetransaction' which according to my research will just add virtual fee and priority and nothing else.
Questions :
1. What is the benefit of adding virtual priority if in reality a tx send with lower fee will always take longer to confirm whether or not it has virtual priority or fee?
Alright. Lets start with the basic concept on what the miner can do. Miners can choose whatever transactions they want to include in the blocks that they mine.
Prioritisetransaction is a client side thing that only appears to your software. Lets say you are a miner and you see that you want transaction A to be confirmed ASAP but you choose to not even pay a fee. In this case, what you can do is to prioritise your transaction using the command (add fee/add priority) and your node will think the transaction has a higher fee/priority.
For that, if your transaction has lets say 0.001BTCfee and 0 priority and is 1kb in size. Adding a virtual fee of 0.1BTC and priority of 100,000,000 will make the transaction appear to have 0.101BTC/KB fee and a priority of 100,000,000. Even if another transaction actually pays 0.09BTC/KB and has a priority of 90,000,000 , your transaction will be included first.
2. What is the actual purpose of this command ? and in under what circumstances an user will feel the need for using this function?
The use is more for miners who want to include specific transactions. A user won't have use for this if that Bitcoin Core node is not used for mining.
It can also be used to make the node think that the priority or the fee is lower than it actually is.
As said, this will not affect the transactions or others, only your Bitcoin Core node which is used for mining.
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