A very great deal.
Slaves were the labour-saving devices of their day.
You want your bread corn ground? Get the slave to do it.
You want your very complicated taxes sorted out? Get your slave accountant to deal with them.
Need the kids taken to school? Get the pedagogue slave to do it.
Want to go watch the gladiators? They were slaves.
Ladies, need your hair done? Get your slave hairdresser to do it.
Garden overgrown? Get the slaves on it.
Slaves were everywhere and did most jobs, mainly those that free Romans didn't want to do, because they were too hard or too boring. Slaves weren't allowed to join the Army, though (they were liable to be executed if they were found out), however, freed slaves (although not the slaves themselves) were allowed to join the Roman Fire Service.
I think the idea of not letting slaves into the Army, the Fleets or the Fire service was because they might get hold of weapons and learn how to use them - and the Romans knew just what a slave with weapons could do - his name was Spartacus!