Well, it is NOT a must but rather, individual practices. I happen to think of this because I came across this situation today.
I was at the the cafe/makan place at Ikea, near the link between Ikano and Ikea. I bought my food and drink and was looking for a place to sit myself down. Unfortunately, there was no place so I had to hold my hot dog and my drink and wait. When a family was done and left the table, they had paper bags, tissues, paper cups all strewn over the table. My friend had to push all those wastes to one side of the table and I use the other side of table to eat. Looking around, I could pretty much confirm that there was no staff to clear the table but Ikea placed a few big bins (like those in McDonalds) near by. Of course, as mentioned, it is NOT a must to practice clearing tables but more of being considerate for the next table user, since there isn't any staff to clear the table. Think about it, eating on one side of the table and looking at the left over whatever's on the other half of the table.
That's why I thought I'd start this poll to check out how many would clear their tables out of consideration and being a nice dude/dudette. :)
Just a side note, even the hot dog was bare plain. Just the hot dog and bun alone. The sauce, mustard, onions, toppings, etc. which you usually find on regular hot dogs are also self service, just like the tomato and chilli sauce in McDonalds, on another separate small section. Soft drinks and coffee are also self service in yet another separate area, like Burger King style.
I used to not clear the table but I figured that it was personally more considerate to clear the table for the next table user. Of course, I don't go to the extent of wiping the table clean. hahaha I just throw away what I used.