that are offshore. They'd also have been fine places for chieftains to discuss boundaries, marriages and truces,no way to sneak up on them and do them in. Celebrations would have been after those events. However, using them to show off in front of the peasants on the shoreline would have been a pretty bad idea.
As for the burned neolithic pot shards, maybe some of them were used for firing the pottery. It makes sense, it's surrounded by water during a time the mainland was heavily forested. If the fire got out of hand, it wouldn't spread. Pots that cracked or broke, and some always do, were just tossed into the drink. There are a lot of crannogs, more than would be necessary as ceremonial or party spots. They might even have been used as habitation for shellfish like mussels, easy harvesting for the local clans.
Wooden platform houses built over still water in marshes, ponds, and lakes were something different, and were as likely to have been constructed for ease of sanitation as well as obtaining water and doing a little fishing as anything else, weirs and fish traps having been found near the excavation at Must Farm. Water during that period was seen as a highway, not a barrier, athought it would have discouraged some of the large predators that didn't swim. It wouldn't have worked on bears, they can swim, although wading would have done the trick in most cases, the water wasn't deep.
We don't know why they did crazy things like knocking themselves out making little artificial islands offshore. It's fun to speculate.