Hi,
centos schedule for daily crond.daily this command:
makewhatis -u -w

do you think that this is an useful job?
may I remove it?

This depends on if you use the 'whatis' command. If you've never used it and will never use it, I see no need to have cron run it. Now, it is not a process-intensive thing to run (if it is run daily, to scale the work), so you can probably leave it running with minimal impact.