Not sure if it applies to H-1B but if a company does mass layoffs, it automatically makes it so that the PERM applications (required for green card, which you need to keep the employee past the visa validity period + extensions; up to 7 years iirc) will be automatically rejected for some time. So it screws over your existing H-1B holders, making your company way less attractive.

Source: I came to the US on H-1B in 2012. I may be misremembering which stage of the process the mass layoffs affect.