There investors that may not want to go in all at once, they may decide to keep some percentage of there discretionary income and them use the remaining percentage for buying the dip. As per being a low coiner ,it also depends on ones cash flow for someone with a good cash flow management that may have a good amount of discretionary income after sorting out all there expenses may decide not to put all there discretion into buying bitcoin at once they can decide to use some percentage to DCA and the remaining percentage for buying the dips.
Going all in at once is not a bad approach or method if the funds you are using to go all in is from your discretionary income because our discretionary income is meant for Bitcoin accumulation but it will be very disastrous and wrong to go all in using money meant for other expenses that is using money outside your discretionary income. and doing this can be seen as a gamble because it implies that you are using the money outside your discretionary income to buy Bitcoin and then hoping or planning to sell soon if there is little increase in the market and this is why some persons panic and sell at loss because when they have this intention and it doesn't go as planned they will panic and sell.
Since somehow this is good move especially if they don't have any plans to diversify or explore on other investment since buying lots of volume would give them a chance to earn more returns on Bitcoin.
It is good to go as aggressive as possible when you are investing in bitcoin as long as you have your discretionary income. However, it seems you are forgetting that in a long-term investment plan, an investor only invests a percentage of your Discretionary income and not all your discretionary income. This is because, your discretionary income is all the money left after taking care of your basic responsibilities. It is a wrong advice to invest all the money because you still have to keep a part of the discretionary income as your backup funds and another percentage of the discretionary income as your emergency funds. This is to ensure the security of your bitcoin and to cushion it against unforeseen circumstances and inflation.
Investing all your discretionary income is very detrimental and can destroy your long-term plan when unforeseen eventualities set in. The best you can do is to increase your percentage of the discretionary income going into bitcoin especially when you have accumulated and emergency funds earlier enough. Instead of maintaining same percentage allocation meant for your emergency funds, you can reduce it to a large extent in order to increase your percentage allocation for your bitcoin investment. By so doing, you would stand better chances of holding your bitcoin for long and whenever your emergency funds are tampered with, your bitcoin stash get exposed to possible danger.
Investing all your discretionary income in bitcoin with little or no emergency funds could cause you to sell off a part of all of your bitcoin when things turn sour.
What I really think will be wrong for doing that is if they put all in on their Bitcoin short term trades since there's really a good chance that they suffer some volatility issues that might cause them to lose their money especially if they get panic easily.
Both Logically
and practically speaking, Bitcoin traders are the real people that invest all their discretionary income into trading at all time because they have a short term plan on their investments. Some gamblers sell of all or a part of their bitcoin in less than 72 hours after investment while others could trade for months too.
Investing all your discretionary income can not let you hold for long due to life exigencies. You have a point but I feel you only got confused about what Discretionary income really is.