Why do you prefer cash secured over selling a put spread?
They are different concepts. You can have cash secured naked vs. margin naked, or cash secured spreads vs. margin spreads. I know you know the difference, but I'm just pointing it out to those on here with less options experience that may not.
But to answer your question, it depends on the time left on the option and the underlying. You need to look at how far the option could go, and understand if you're alright with that level of loss or not. If not, I'll turn it into a spread over naked.
Some examples may help.
1. I sell an SPY put, -10 delta. SPY is currently sitting at 452.76. The option expiring Tuesday (9/7) -10 delta put would be the 448 put, selling for $0.15. Now I could sell that option, cash secured, which would require me to hold onto $44,800 in cash in the event I'm assigned. But SPY has a floor in a 1 day move. It can only drop 20% before trading would be halted. Which means at worst, SPY would hit $362. So I don't need the full $44,800, as my max loss is $8,600. I could reduce my max loss to $1,000 by turning it into a spread and buying the 438 for $0.05, but it also cuts out 1/3rd my potential profit. And I'm only buying protection for an event where SPY drops MORE THAN 3.2% in a single day. The odds are really small it will move more than 3% in a day. What you'll find is when you have a loss, SPY will often move lower than your sold put, but not low enough for the buy put to make a difference. Which just means you're leaving cash on the table. So if SPY drops 3% in one day, the person that sold the naked put and the person that sold the 10 pt spread have the same loss ($1,000), but the naked made 33% more on every day the SPY didn't drop 3%.
2. I sell an SPX put, -10 delta. SPX is currently sitting at 4,535.43. The option expiring Tuesday (9/7) -10 delta put would be the 4,480 put, selling for $1.95 (mid). SPX has the same 1 day floor. So cash secured would require me to hold onto $448,000 in cash. Max loss (20% drop) would "only" be $85,200. Realistically speaking, the market rarely drops more than 3% in a day, so my real life possible loss is closer to $8,000, although it obviously isn't limited to that. Same analysis as above, but with more money involved. If I wanted to keep it as cash secured, but didn't feel comfortable with $448,000 being held in cash to make a max of $195, I could buy a leg to free up my cash secured requirements. But it cuts into my profitability. Again, absent a dooms day event, the naked and the spread seller will have the same realized loss, but the naked seller will make more. By making more, they can better withstand the loss whenever a greater than 3% loss day does come.
Note: for both above, buying a leg reduces your max loss, but increases the probability that you'll hit your max loss. For example, a naked SPY put may have a max loss $8,600, but it requires a single day 20% drop which occurred what, once ever? Or I could turn it into a spread, but I would hit my max loss of $1,000 if a 3.2% one day drop occurs, which has happened thousands of times in the past 100 years. With this strategy you need to be able to survive multiple drops and keep playing. If you have, say $10,000 to invest, you could go with one naked or 10 spreads. And it's so easy to ramp it up to 10 spreads. But when that 3.2% down day comes, naked takes a loss and keeps rolling while the 10 spreads files bankruptcy. So the goal is NOT to trade more spreads than naked, just because the collateral requirement is less.
3. I sell an SPX put, -10 delta. SPX is currently sitting at 4,535.43. This time, instead of looking at the 1 dte option, I look at the 7 dte option (expiring 9/13). The -10 delta put is the 4415 strike, for $4.2. Cash secured would still require $441,500 in cash in the account, but this time my "real" max loss is different. The 4415 strike is 2.6% OTM. It also gives me 5 days of possibilities. So in theory, I could have 5 straight days of a 20% drop each (incredibly unlikely, obviously), which means my "real" max loss is closer to $304,900 (forget for a second that if the market dropped 20% each day for 5 straight days, we're probably living in a "Mad Max" type world, where money in accounts is meaningless). Not only that, but if I see a 5% drop on ANY day in the next 5 days, I hit my max loss. So the odds are a little different. In that instance, I could buy a 50 pt leg, and it'll cost me $3.00. Max loss is $5,000, and max profit is $1.20. A better risk to return rate than the 1 dte option in #2 above. So the spread makes more sense.
In the end, spreads allow you to reduce your potential max loss, but increase the probability you'll hit the max loss. Spreads reduce your profit potential too, but may allow you to sleep better at night. I do both though, depending on how far OTM the short strike is, how many days are left, and how much risk I find acceptable.