On lifetime deals specifically, since they turn up in every launch discussion: be extremely careful, and understand what you are actually selling.
A lifetime deal is not a discount. It is you taking a small amount of money now in exchange for an unbounded obligation, support, hosting, updates, forever: from the customers least likely to be a good fit.
What happened to me: a hundred or so lifetime buyers at a low price. Two years later they are a meaningful share of my support load, a meaningful share of my hosting cost, and zero of my revenue. They also, entirely reasonably, expect the product to keep improving.
When it can make sense:
When you genuinely need cash now and are clear-eyed that you are borrowing against future revenue.
When the marginal cost per customer is near zero and you cap the number sold.
When it is capped and time-limited, so the obligation is bounded.
What makes it dangerous: uncapped, on a product with real per-customer costs, sold to people who wanted a bargain rather than the product.
If you do it, cap it hard: a specific number, stated: and price it at something like two to three years of the subscription, not two months.