What do people mean when they say to hold on to bitcoin? If someone wanted to spend 300k usd of bitcoin should they spend this amount as soon as they have it or wait longer until its worth a lot more than just 300k usd? How can this be determined?
If you have such amount in Bitcoin, it's completely up to you on how you want to spend it. If you want to hold x number of years, it's your asset and you should make the decision on how long you want to hold. The reason why you are advised to hold is because you will get more profit if you continue to hold. For example, if you had bought 1 Bitcoin for $20k in the past four years and you hold till this year, you would have got $80k+ as profit. That's the advantage of holding.