Does it make sense to have a fixed amount in an ETF over time?

For example $5k of SOXQ where I trim every 3 to 6 months. It's long term but technically a diminishing part of the portfolio over time. I was curious about the math. If you do not allow it to compound, is that an opportunity cost as opposed to staying invested in it? I don't have many ETFs but was wandering if you had something like that "outside" the portfolio. Instead of "5% FBTC", your portfolio has "$10k of shares". Reason? To keep things tidy... but is this mis

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