Unfortunately mactec54 is incorrect; Haas machines have no provision for being bolted down and with some of them it is completely unnecessary.
You are going to find this issue argued up, down and sideways.
On big machines which are very precise a separate isolated foundation block is essential to attain the full accuracy and precision the machine is capable of. The isolation is from the building floor pad, this is cut out, a large hole is excavated, with luck to a good solid base, and then this is filled and rammed with roadbase material and a concrete block poured. As mentioned the mass of the concrete should be heavier than the machine. It is a moot point whether the machine should be bolted down to the block. If the machine is capable of very high speed rapids with large masses of fixturing and parts on the table then it probably should be bolted and will probably have bolt pads not just leveling pads.
At the other end of the spectrum with a machine like a Haas MiniMill it does not even need to be levelled; it does not even need to be sitting on all four feet! However, if it is not it will rock and make annoying noises.
I have gone through this thing about bolting machines down back and forth with people for over forty years. I ran turret lathes ranging from 3500lb weight up to 20,000lbs and none were bolted down. Once I moved a big one to a new location while it was set up for a particular job, merely shimmed all the floor contact points so it didn't wobble without levelling the machine and the first part made after the move was within 0.0005" of the last part before the move.
On some big machines like big shaft turning lathes where the workpiece may be approaching the weight of the machine they have to be bolted down to concrete foundation blocks otherwise the machine might start walking around when it is spinning an out of balance shaft. In this situation the foundations really become part of the machine, and because they settle the machine must be re-aligned and levelled frequently. I live on a river delta and one big machine shop here could only run their biggest lathe at its best precision when the tide was at a particular level because the ground moved with the ebbing and flowing water.
But, having said all this, you are bound to find people who will argue dogmatically one way or the other.
An open mind is a virtue...so long as all the common sense has not leaked out.