Yep, as Dodgeman said above, not using the spacer will cause the rear suspension to have a small amount of toe in along with the attendant slight misalignment of the axle splines in the differential carrier and wheel bearings. Doing some quick calculations it looks like the toe in caused by moving the center of the axles rearward by 2.5mm assuming 558mm (22") length between the differential and wheel bearing would come out to be just under .25 degrees.

Back in the late '70's I saw a Chevy Camero at PIR (Portland International Raceway) that looked like it has negative camber on the rear wheels, a interesting trick as the Camero had a straight axle like the 1200's do. Talking to the team they had used a porta-power to actually bend the axle housing down in the middle enough to get about 3/4 degree negative camber on the rear wheels. Said the axle splines held up for several races before they replaced them. This was in a car that was putting close to 500HP on the ground.

How much will a quarter of a degree of toe in will effect the handling? I don't know...