I have mine set the same and it is perfect for 95% of the time as the 0.5mm allows the material to just float along. It is only a problem when cutting veneered panels etc when the 0.5mm can be a problem for spelching (I do not have a scoring unit) but I just use a piece of 12mm pdf as a zero clearance sub table. It can also be a problem machining wide boards on the spindle.I use a Felder saw with a sliding table, but actually these same general principles apply to all sliding tables.
If you're chiefly using the sliding table to cut sheet goods, then you're best off with the sliding table slightly higher than the main table. Felder/Hammer recognise this and therefore the sliding tables are fully adjustable. Most workshops I know seem to set this gap at about 0.5mm, but I've seen gaps up to 3mm. This reason is that this makes it easier to transport "floppy" sheet goods like MDF across the saw. If you've ever ganged up a stack of say 20 hardboard sheets for cutting wardrobe backs then trust me, you'll really appreciate a gap that's towards the larger end of the spectrum! I understand some joiners who are using resinous softwoods, particularly if they're not always as well kilned as they might be, also prefer a larger gap.
On the other hand, if you mainly use your saw for hardwood furniture then you'll probably go for a smaller gap or even no gap at all (ie dead flush). However, note that the risks are asymmetric, in other words a tiny gap with a higher sliding table is no big deal, but the same tiny gap with the main table higher makes sawing difficult and is potentially dangerous. Furthermore, with very small gaps you're also into the zone of how flat are your tables? In other words you want a safety margin across the full travel of the slider and the full width of the table.
Consequently, even though I chiefly use kilned hardwoods, I have my sliding table 0.5mm higher than the fixed table and I'm a happy camper.
Hope that helps.