Discounts widen with deal size relative to average volume, with volatility, and with how much the buyers distrust the seller. A liquid large cap might place stock at a 2% discount; a micro cap raising a quarter of its market value may pay 20% plus warrants.
Traders use the offer price as a reference level for days afterwards. It is where the new holders' cost basis sits, so it often acts as both support and a supply ceiling.
Example: a stock closes at $24.00 and the deal prices at $22.80. The discount is $1.20 / $24.00 = 5%. Buyers of a 12M share deal receive $14.4M of immediate paper gain relative to the prior close.
Related: follow-on-offering, secondary-offering, underwriter, dilution, rights-issue