Litespeed still faster even without LS cache being enabled. LS cache is page cache for dynamic script like php. if your server have more resources to spare and want even more faster speed, then you can use LS cache.
you can enable private cache for caching each account's php script. no tweaks required to their htaccess. however, if each account needs different cache expire time, tweaking is needed in their htaccess to override general cache policy settings.