The htcachclean daemon is a common Apache component that is there to keep the cache of the MAC defs on the SEPM at a reasonable size. Without it, the cache will grow unchecked over time (i.e. even files that are no longer required will still be kept). The command you posted tells it to run in deamon mode, check the cache every 1 day, and bring it down to 1GB in size if over.
Check out the below description of it from the the interwebs:
http://httpd.apache.org/docs/2.4/programs/htcacheclean.html
"htcacheclean
is used to keep the size of mod_cache_disk
's storage within a given size limit, or limit on inodes in use. This tool can run either manually or in daemon mode. When running in daemon mode, it sleeps in the background and checks the cache directory at regular intervals for cached content to be removed...."