Depends on the machine design.
If the lathe is old and was made with legs at each end of the bed like a saw horse, attachment fastener torque will have little effect on the bed's linearity or alignment so long as the gap to be closed is not eccessive..
If the lathe is a more modern design where the bed sits on pedistals, little improvement will be gained by scraping the faying surfaces on the tailstock end (or intermediate pedistals if equipped) but the headstck end is usually rigid box shaped casting and has a much larger face in contact with the bottom of the bed. If a simple dress with file and stone to remove burrs doesn't eliminate gaps, scraping to close the joint all around is an opition but with limits. I suggest 0.004 as the max gap to disregard (this is a moving target where much depends on the size and rigidity of the pedistal casting and the bed.) Over 0.004" gap chould probably be closed by drawing up the bolts. Scraping is certainly the gold standard but this is an assembly joint where shim washers fitted to fill the gap at each bolt hole is a valid fix.
Heavy duty lathes where the bed is attached to a rigid one-piece base casting poses a dilemma. Supposedly the factory fits the all-but-finished bed to the base where the joints are interrogated with a 0.001" (0.025 mm) feeler and any discrepancies are remedied before the way surfaces are scraped/finish ground. If your lathe has a gap in the headstock pedestal joint, it must be determined if the bed linearity is improved or not by closing the gap. This can lead to quite a program of checking and fitting.
I've been bitten by this snake re-grinding the bed of an 18" Okuma lathe whose bed was rigidly bolted and pinned to a sturdy cast iron base making a very stiff assembly. The customer sent only the bed without the base and the bed did not sit flat on the grinder table - there were wedge shaped gaps on the base connection faces. The decision from the white hats was to shim to neutral stress and grind it. We didn't get a complaint so the assumption was the bosses made a good call but I was never happy with their decision. Shoulda fetched in the base just to be sure.