This is a thought I've had for quiet a while and can't figure out how I would Google the answer nor the math.
If I theoretically had a multi coin wallet with 0% in-wallet trading fees could you play the difference between Bitcoin in a meger day versus an alt bin a good day.
For example I have 1 BTC which went up 1% to $10,000 in the last 12hrs as well as 5 Ethereum which spiked up 15% to $500. Thus if I notice this on the "trade between BTC ETH & XMR free" website and traded my 5 eth for 2500$ of BTC or 0.25 BTC. Would I have made a profit if the charts stabilize them back to 0&0% gains a week later after the market plays with it.
Indeed you will make profit in this scenario as you will have more units of Bitcoin than before.
Let me simplify the scenario for you. Suppose you had 1 BTC worth $10000 and 5 ETH worth $2000 each or $10000 in total. So your total holding worth 2 BTC.
Now suppose price of Bitcoin rose by 10% and of ETH by 20%. So if you sell all your ETH, you will get 1.09 BTC. Now your total holding would worth $23000 and you will have 2.09 BTC.
Now again suppose gains of both coins come back to 0-0%. So BTC will worth $10000 once again but since you have 0.09 additional units of BTC, you made profit of $900 in the process on your initial capital.
However, no wallet provide free of cost intra-wallet trade in my knowledge.