If the goal is just to buy and hold, then you wouldn't use perps, not only because of counterparty risk but also because the funding rate is typically positive, meaning you pay (usually ~10% APR) to be long.

The point of perps is:

- Easy access to leverage. Unlike options or futures, there's no need to roll over.

- It's the easiest way to short a coin. Most of the time you even get paid the funding rate to be short.

- Trading fees are typically much lower than for spot.

- Volume and liquidity can be better for perps than for spot. The BTC/USDT perp did 10x the volume of the spot pair in the last 24h on Binance.

Because the exchanges offer 20x leverage on perps but not on spot. In theory perps can have deeper liquidity because they can go beyond the 21M BTC limit. If you don't care about those factors then you shouldn't trade perps; they aren't intended to be magically superior to spot.

You want to buy bitcoin to be a bitcoin investor. But if you want to actively trade, both buy and sell, futures offer much more capital efficient solution. With leverage, you can make larger trades with less money.

You can buy (go long) a BTC future with only $10,000 or less of collateral. So you can get lots of leverage.

Another reason is that the future may be trading slightly below the spot price of BTC due to lots of traders shorting.

A perp is a future which is different from buying BTC at its spot price. If you remove the "perpetual" aspect of the future and it was a regular future that was settling soon, likewise it would be similar in price but not the same as the underlying. There's lots of uses for futures and they're often used as hedges against various forms of risk, like currency risk.

maybe to avoid checking a box on an irs form?

You are getting leverage. Leverage and liquidity are the reasons you deal in futures.